The Lustre architecture is a storage architecture for clusters. The central component of the Lustre architecture is the Lustre file system, which is supported on the Linux operating system and provides a POSIX ^*standard-compliant UNIX file system interface.

The Lustre storage architecture is used for many different kinds of clusters. It is best known for powering many of the largest high-performance computing (HPC) clusters worldwide, with tens of thousands of client systems, petabytes (PB) of storage and hundreds of gigabytes per second (GB/sec) of I/O throughput. Many HPC sites use a Lustre file system as a site-wide global file system, serving dozens of clusters.

The ability of a Lustre file system to scale capacity and performance for any need reduces the need to deploy many separate file systems, such as one for each compute cluster. Storage management is simplified by avoiding the need to copy data between compute clusters. In addition to aggregating storage capacity of many servers, the I/O throughput is also aggregated and scales with additional servers. Moreover, throughput and/or capacity can be easily increased by adding servers dynamically.

While a Lustre file system can function in many work environments, it is not necessarily the best choice for all applications. It is best suited for uses that exceed the capacity that a single server can provide, though in some use cases, a Lustre file system can perform better with a single server than other file systems due to its strong locking and data coherency.

A Lustre file system is currently not particularly well suited for "peer-to-peer" usage models where clients and servers are running on the same node, each sharing a small amount of storage, due to the lack of data replication at the Lustre software level. In such uses, if one client/server fails, then the data stored on that node will not be accessible until the node is restarted.

An installation of the Lustre software includes a management server (MGS) and one or more Lustre file systems interconnected with Lustre networking (LNet).

A basic configuration of Lustre file system components is shown in Figure 1.1, “Lustre file system components in a basic cluster”.

Figure 1.1. Lustre file system components in a basic cluster

1.2.4.  Lustre Cluster

At scale, a Lustre file system cluster can include hundreds of OSSs and thousands of clients (see Figure 1.2, “ Lustre cluster at scale”). More than one type of network can be used in a Lustre cluster. Shared storage between OSSs enables failover capability. For more details about OSS failover, see Chapter 3, Understanding Failover in a Lustre File System.

Figure 1.2.  Lustre cluster at scale

In Lustre software release 2.0, Lustre file identifiers (FIDs) were introduced to replace UNIX inode numbers for identifying files or objects. A FID is a 128-bit identifier that contains a unique 64-bit sequence number, a 32-bit object ID (OID), and a 32-bit version number. The sequence number is unique across all Lustre targets in a file system (OSTs and MDTs). This change enabled future support for multiple MDTs (introduced in Lustre software release 2.4) and ZFS (introduced in Lustre software release 2.4).

Also introduced in release 2.0 is an ldiskfs feature named FID-in-dirent(also known as dirdata) in which the FID is stored as part of the name of the file in the parent directory. This feature significantly improves performance for ls command executions by reducing disk I/O. The FID-in-dirent is generated at the time the file is created.

Information about where file data is located on the OST(s) is stored as an extended attribute called layout EA in an MDT object identified by the FID for the file (see Figure 1.3, “Layout EA on MDT pointing to file data on OSTs”). If the file is a regular file (not a directory or symbol link), the MDT object points to 1-to-N OST object(s) on the OST(s) that contain the file data. If the MDT file points to one object, all the file data is stored in that object. If the MDT file points to more than one object, the file data is striped across the objects using RAID 0, and each object is stored on a different OST. (For more information about how striping is implemented in a Lustre file system, see Section 1.3.1, “ Lustre File System and Striping”.

Figure 1.3. Layout EA on MDT pointing to file data on OSTs

When a client wants to read from or write to a file, it first fetches the layout EA from the MDT object for the file. The client then uses this information to perform I/O on the file, directly interacting with the OSS nodes where the objects are stored. This process is illustrated in Figure 1.4, “Lustre client requesting file data” .

Figure 1.4. Lustre client requesting file data

The available bandwidth of a Lustre file system is determined as follows:

1.3.1.  Lustre File System and Striping

One of the main factors leading to the high performance of Lustre file systems is the ability to stripe data across multiple OSTs in a round-robin fashion. Users can optionally configure for each file the number of stripes, stripe size, and OSTs that are used.

Striping can be used to improve performance when the aggregate bandwidth to a single file exceeds the bandwidth of a single OST. The ability to stripe is also useful when a single OST does not have enough free space to hold an entire file. For more information about benefits and drawbacks of file striping, see Section 18.2, “ Lustre File Layout (Striping) Considerations”.

Striping allows segments or 'chunks' of data in a file to be stored on different OSTs, as shown in Figure 1.5, “File striping on a Lustre file system”. In the Lustre file system, a RAID 0 pattern is used in which data is "striped" across a certain number of objects. The number of objects in a single file is called the stripe_count.

Each object contains a chunk of data from the file. When the chunk of data being written to a particular object exceeds the stripe_size, the next chunk of data in the file is stored on the next object.

Default values for stripe_count and stripe_size are set for the file system. The default value for stripe_count is 1 stripe for file and the default value for stripe_size is 1MB. The user may change these values on a per directory or per file basis. For more details, see Section 18.3, “Setting the File Layout/Striping Configuration (lfs setstripe)”.

Figure 1.5, “File striping on a Lustre file system”, the stripe_size for File C is larger than the stripe_size for File A, allowing more data to be stored in a single stripe for File C. The stripe_count for File A is 3, resulting in data striped across three objects, while the stripe_count for File B and File C is 1.

No space is reserved on the OST for unwritten data. File A in Figure 1.5, “File striping on a Lustre file system”.

Figure 1.5. File striping on a Lustre file system

The maximum file size is not limited by the size of a single target. In a Lustre file system, files can be striped across multiple objects (up to 2000), and each object can be up to 16 TB in size with ldiskfs, or up to 256PB with ZFS. This leads to a maximum file size of 31.25 PB for ldiskfs or 8EB with ZFS. Note that a Lustre file system can support files up to 2^63 bytes (8EB), limited only by the space available on the OSTs.

Note

Versions of the Lustre software prior to Release 2.2 limited the maximum stripe count for a single file to 160 OSTs.

Although a single file can only be striped over 2000 objects, Lustre file systems can have thousands of OSTs. The I/O bandwidth to access a single file is the aggregated I/O bandwidth to the objects in a file, which can be as much as a bandwidth of up to 2000 servers. On systems with more than 2000 OSTs, clients can do I/O using multiple files to utilize the full file system bandwidth.

For more information about striping, see Chapter 18, Managing File Layout (Striping) and Free Space.

In a cluster using one or more Lustre file systems, the network communication infrastructure required by the Lustre file system is implemented using the Lustre networking (LNet) feature.

LNet supports many commonly-used network types, such as InfiniBand and IP networks, and allows simultaneous availability across multiple network types with routing between them. Remote direct memory access (RDMA) is permitted when supported by underlying networks using the appropriate Lustre network driver (LND). High availability and recovery features enable transparent recovery in conjunction with failover servers.

An LND is a pluggable driver that provides support for a particular network type, for example ksocklnd is the driver which implements the TCP Socket LND that supports TCP networks. LNDs are loaded into the driver stack, with one LND for each network type in use.

For information about configuring LNet, see Chapter 9, Configuring Lustre Networking (LNet).

For information about administering LNet, see Part III, “Administering Lustre”.

Key features of LNet include:

LNet permits end-to-end read/write throughput at or near peak bandwidth rates on a variety of network interconnects.

A Lustre network is comprised of clients and servers running the Lustre software. It need not be confined to one LNet subnet but can span several networks provided routing is possible between the networks. In a similar manner, a single network can have multiple LNet subnets.

The Lustre networking stack is comprised of two layers, the LNet code module and the LND. The LNet layer operates above the LND layer in a manner similar to the way the network layer operates above the data link layer. LNet layer is connectionless, asynchronous and does not verify that data has been transmitted while the LND layer is connection oriented and typically does verify data transmission.

LNets are uniquely identified by a label comprised of a string corresponding to an LND and a number, such as tcp0, o2ib0, or o2ib1, that uniquely identifies each LNet. Each node on an LNet has at least one network identifier (NID). A NID is a combination of the address of the network interface and the LNet label in the form:address@LNet_label.

Examples:

192.168.1.2@tcp0
10.13.24.90@o2ib1

In certain circumstances it might be desirable for Lustre file system traffic to pass between multiple LNets. This is possible using LNet routing. It is important to realize that LNet routing is not the same as network routing. For more details about LNet routing, see Chapter 9, Configuring Lustre Networking (LNet)

The LNet code module includes LNDs to support many network types including:

In a high-availability (HA) system, unscheduled downtime is minimized by using redundant hardware and software components and software components that automate recovery when a failure occurs. If a failure condition occurs, such as the loss of a server or storage device or a network or software fault, the system's services continue with minimal interruption. Generally, availability is specified as the percentage of time the system is required to be available.

Availability is accomplished by replicating hardware and/or software so that when a primary server fails or is unavailable, a standby server can be switched into its place to run applications and associated resources. This process, called failover, is automatic in an HA system and, in most cases, completely application-transparent.

A failover hardware setup requires a pair of servers with a shared resource (typically a physical storage device, which may be based on SAN, NAS, hardware RAID, SCSI or Fibre Channel (FC) technology). The method of sharing storage should be essentially transparent at the device level; the same physical logical unit number (LUN) should be visible from both servers. To ensure high availability at the physical storage level, we encourage the use of RAID arrays to protect against drive-level failures.

The failover functionality provided by the Lustre software can be used for the following failover scenario. When a client attempts to do I/O to a failed Lustre target, it continues to try until it receives an answer from any of the configured failover nodes for the Lustre target. A user-space application does not detect anything unusual, except that the I/O may take longer to complete.

Failover in a Lustre file system requires that two nodes be configured as a failover pair, which must share one or more storage devices. A Lustre file system can be configured to provide MDT or OST failover.

The --servicenode option is used to set up nodes in a Lustre file system for failover at creation time (using mkfs.lustre) or later when the Lustre file system is active (using tunefs.lustre). For explanations of these utilities, see Section 38.14, “ mkfs.lustre”and Section 38.18, “ tunefs.lustre”.

Failover capability in a Lustre file system can be used to upgrade the Lustre software between successive minor versions without cluster downtime. For more information, see Chapter 16, Upgrading a Lustre File System.

For information about configuring failover, see Chapter 11, Configuring Failover in a Lustre File System.

3.2.1.  MDT Failover Configuration (Active/Passive)

Two MDSs are typically configured as an active/passive failover pair as shown in Figure 3.1, “Lustre failover configuration for a active/passive MDT”. Note that both nodes must have access to shared storage for the MDT(s) and the MGS. The primary (active) MDS manages the Lustre system metadata resources. If the primary MDS fails, the secondary (passive) MDS takes over these resources and serves the MDTs and the MGS.

Note

In an environment with multiple file systems, the MDSs can be configured in a quasi active/active configuration, with each MDS managing metadata for a subset of the Lustre file system.

Figure 3.1. Lustre failover configuration for a active/passive MDT

Introduced in Lustre 2.4

3.2.2.  MDT Failover Configuration (Active/Active)

Multiple MDTs became available with the advent of Lustre software release 2.4. MDTs can be setup as an active/active failover configuration. A failover cluster is built from two MDSs as shown in Figure 3.2, “Lustre failover configuration for a active/active MDTs”.

Figure 3.2. Lustre failover configuration for a active/active MDTs

3.2.3.  OST Failover Configuration (Active/Active)

OSTs are usually configured in a load-balanced, active/active failover configuration. A failover cluster is built from two OSSs as shown in Figure 3.3, “Lustre failover configuration for an OSTs”.

Note

OSSs configured as a failover pair must have shared disks/RAID.

Figure 3.3. Lustre failover configuration for an OSTs

In an active configuration, 50% of the available OSTs are assigned to one OSS and the remaining OSTs are assigned to the other OSS. Each OSS serves as the primary node for half the OSTs and as a failover node for the remaining OSTs.

In this mode, if one OSS fails, the other OSS takes over all of the failed OSTs. The clients attempt to connect to each OSS serving the OST, until one of them responds. Data on the OST is written synchronously, and the clients replay transactions that were in progress and uncommitted to disk before the OST failure.

For more information about configuring failover, see Chapter 11, Configuring Failover in a Lustre File System.

To set up Lustre file system hardware and install and configure the Lustre software, refer the the chapters below in the order listed:

A Lustre file system can utilize any kind of block storage device such as single disks, software RAID, hardware RAID, or a logical volume manager. In contrast to some networked file systems, the block devices are only attached to the MDS and OSS nodes in a Lustre file system and are not accessed by the clients directly.

Since the block devices are accessed by only one or two server nodes, a storage area network (SAN) that is accessible from all the servers is not required. Expensive switches are not needed because point-to-point connections between the servers and the storage arrays normally provide the simplest and best attachments. (If failover capability is desired, the storage must be attached to multiple servers.)

For a production environment, it is preferable that the MGS have separate storage to allow future expansion to multiple file systems. However, it is possible to run the MDS and MGS on the same machine and have them share the same storage device.

For best performance in a production environment, dedicated clients are required. For a non-production Lustre environment or for testing, a Lustre client and server can run on the same machine. However, dedicated clients are the only supported configuration.

Only servers running on 64-bit CPUs are tested and supported. 64-bit CPU clients are typically used for testing to match expected customer usage and avoid limitations due to the 4 GB limit for RAM size, 1 GB low-memory limitation, and 16 TB file size limit of 32-bit CPUs. Also, due to kernel API limitations, performing backups of Lustre software release 2.x. file systems on 32-bit clients may cause backup tools to confuse files that have the same 32-bit inode number.

The storage attached to the servers typically uses RAID to provide fault tolerance and can optionally be organized with logical volume management (LVM), which is then formatted as a Lustre file system. Lustre OSS and MDS servers read, write and modify data in the format imposed by the file system.

The Lustre file system uses journaling file system technology on both the MDTs and OSTs. For a MDT, as much as a 20 percent performance gain can be obtained by placing the journal on a separate device.

The MDS can effectively utilize a lot of CPU cycles. A minimum of four processor cores are recommended. More are advisable for files systems with many clients.

The desired performance characteristics of the backing file systems on the MDT and OSTs are independent of one another. The size of the MDT backing file system depends on the number of inodes needed in the total Lustre file system, while the aggregate OST space depends on the total amount of data stored on the file system. If MGS data is to be stored on the MDT device (co-located MGT and MDT), add 100 MB to the required size estimate for the MDT.

Each time a file is created on a Lustre file system, it consumes one inode on the MDT and one OST object over which the file is striped. Normally, each file's stripe count is based on the system-wide default stripe count. However, this can be changed for individual files using the lfs setstripe option. For more details, see Chapter 18, Managing File Layout (Striping) and Free Space.

In a Lustre ldiskfs file system, all the MDT inodes and OST objects are allocated when the file system is first formatted. When the file system is in use and a file is created, metadata associated with that file is stored in one of the pre-allocated inodes and does not consume any of the free space used to store file data. The total number of inodes on a formatted ldiskfs MDT or OST cannot be easily changed. Thus, the number of inodes created at format time should be generous enough to anticipate near term expected usage, with some room for growth without the effort of additional storage.

By default, the ldiskfs file system used by Lustre servers to store user-data objects and system data reserves 5% of space that cannot be used by the Lustre file system. Additionally, an ldiskfs Lustre file system reserves up to 400 MB on each OST, and up to 4GB on each MDT for journal use and a small amount of space outside the journal to store accounting data. This reserved space is unusable for general storage. Thus, at least this much space will be used per OST before any file object data is saved.

By default, the mkfs.lustre utility applies these options to the Lustre backing file system used to store data and metadata in order to enhance Lustre file system performance and scalability. These options include:

To override the default formatting options, use arguments to mkfs.lustre to pass formatting options to the backing file system:

--mkfsoptions='backing fs options'

For other mkfs.lustre options, see the Linux man page for mke2fs(8).

[oss#] mkfs.lustre --ost --mkfsoptions="-i $((8192 * 1024))" ...

This section describes the memory requirements for each Lustre file system component.

As a high performance file system, the Lustre file system places heavy loads on networks. Thus, a network interface in each Lustre server and client is commonly dedicated to Lustre file system traffic. This is often a dedicated TCP/IP subnet, although other network hardware can also be used.

A typical Lustre file system implementation may include the following:

Lustre networks and routing are configured and managed by specifying parameters to the Lustre Networking (lnet) module in /etc/modprobe.d/lustre.conf.

To prepare to configure Lustre networking, complete the following steps:

The Lustre architecture allows the use of any kind of block device as backend storage. The characteristics of such devices, particularly in the case of failures, vary significantly and have an impact on configuration choices.

This section describes issues and recommendations regarding backend storage.

RAID monitoring software is recommended to quickly detect faulty disks and allow them to be replaced to avoid double failures and data loss. Hot spare disks are recommended so that rebuilds happen without delays.

Backups of the metadata file systems are recommended. For details, see Chapter 17, Backing Up and Restoring a File System.

A writeback cache can dramatically increase write performance on many types of RAID arrays if the writes are not done at full stripe width. Unfortunately, unless the RAID array has battery-backed cache (a feature only found in some higher-priced hardware RAID arrays), interrupting the power to the array may result in out-of-sequence writes or corruption of RAID parity and future data loss.

If writeback cache is enabled, a file system check is required after the array loses power. Data may also be lost because of this.

Therefore, we recommend against the use of writeback cache when data integrity is critical. You should carefully consider whether the benefits of using writeback cache outweigh the risks.

When formatting an ldiskfs file system on a RAID device, it can be beneficial to ensure that I/O requests are aligned with the underlying RAID geometry. This ensures that Lustre RPCs do not generate unnecessary disk operations which may reduce performance dramatically. Use the --mkfsoptions parameter to specify additional parameters when formatting the OST or MDT.

For RAID 5, RAID 6, or RAID 1+0 storage, specifying the following option to the --mkfsoptions parameter option improves the layout of the file system metadata, ensuring that no single disk contains all of the allocation bitmaps:

-E stride = chunk_blocks 

The chunk_blocks variable is in units of 4096-byte blocks and represents the amount of contiguous data written to a single disk before moving to the next disk. This is alternately referred to as the RAID stripe size. This is applicable to both MDT and OST file systems.

For more information on how to override the defaults while formatting MDT or OST file systems, see Section 5.3, “ Setting ldiskfs File System Formatting Options ”.

stripe_width_blocks = chunk_blocks * number_of_data_disks = 1 MB 

--mkfsoptions "other_options -E stride=chunk_blocks, stripe_width=stripe_width_blocks"

--mkfsoptions "other_options -E stride=chunk_blocks, stripe_width=stripe_width_blocks"...

--mkfsoptions "other_options -j -J device=/dev/mdJ" 

Depending on your cluster size and workload, you may want to connect a SAN to a Lustre file system. Before making this connection, consider the following:

Bonding, also known as link aggregation, trunking and port trunking, is a method of aggregating multiple physical network links into a single logical link for increased bandwidth.

Several different types of bonding are available in the Linux distribution. All these types are referred to as 'modes', and use the bonding kernel module.

Modes 0 to 3 allow load balancing and fault tolerance by using multiple interfaces. Mode 4 aggregates a group of interfaces into a single virtual interface where all members of the group share the same speed and duplex settings. This mode is described under IEEE spec 802.3ad, and it is referred to as either 'mode 4' or '802.3ad.'

The most basic requirement for successful bonding is that both endpoints of the connection must be capable of bonding. In a normal case, the non-server endpoint is a switch. (Two systems connected via crossover cables can also use bonding.) Any switch used must explicitly handle 802.3ad Dynamic Link Aggregation.

The kernel must also be configured with bonding. All supported Lustre kernels have bonding functionality. The network driver for the interfaces to be bonded must have the ethtool functionality to determine slave speed and duplex settings. All recent network drivers implement it.

To verify that your interface works with ethtool, run:

# which ethtool
/sbin/ethtool
 
# ethtool eth0
Settings for eth0:
           Supported ports: [ TP MII ]
           Supported link modes:   10baseT/Half 10baseT/Full
                                   100baseT/Half 100baseT/Full
           Supports auto-negotiation: Yes
           Advertised link modes:  10baseT/Half 10baseT/Full
                                   100baseT/Half 100baseT/Full
           Advertised auto-negotiation: Yes
           Speed: 100Mb/s
           Duplex: Full
           Port: MII
           PHYAD: 1
           Transceiver: internal
           Auto-negotiation: on
           Supports Wake-on: pumbg
           Wake-on: d
           Current message level: 0x00000001 (1)
           Link detected: yes
 
# ethtool eth1
 
Settings for eth1:
   Supported ports: [ TP MII ]
   Supported link modes:   10baseT/Half 10baseT/Full
                           100baseT/Half 100baseT/Full
   Supports auto-negotiation: Yes
   Advertised link modes:  10baseT/Half 10baseT/Full
   100baseT/Half 100baseT/Full
   Advertised auto-negotiation: Yes
   Speed: 100Mb/s
   Duplex: Full
   Port: MII
   PHYAD: 32
   Transceiver: internal
   Auto-negotiation: on
   Supports Wake-on: pumbg
   Wake-on: d
   Current message level: 0x00000007 (7)
   Link detected: yes
   To quickly check whether your kernel supports bonding, run:     
   # grep ifenslave /sbin/ifup
   # which ifenslave
   /sbin/ifenslave

Bonding module parameters control various aspects of bonding.

Outgoing traffic is mapped across the slave interfaces according to the transmit hash policy. We recommend that you set the xmit_hash_policy option to the layer3+4 option for bonding. This policy uses upper layer protocol information if available to generate the hash. This allows traffic to a particular network peer to span multiple slaves, although a single connection does not span multiple slaves.

$ xmit_hash_policy=layer3+4

The miimon option enables users to monitor the link status. (The parameter is a time interval in milliseconds.) It makes an interface failure transparent to avoid serious network degradation during link failures. A reasonable default setting is 100 milliseconds; run:

$ miimon=100

For a busy network, increase the timeout.

To set up bonding:

# cat /etc/modprobe.d/bond.conf
alias eth0 8139too
alias eth1 via-rhine
alias bond0 bonding
options bond0 mode=balance-alb miimon=100
 
# cat /etc/sysconfig/network-scripts/ifcfg-bond0
DEVICE=bond0
BOOTPROTO=none
NETMASK=255.255.255.0
IPADDR=192.168.10.79 # (Assign here the IP of the bonded interface.)
ONBOOT=yes
USERCTL=no
 
ifcfg-ethx 
# cat /etc/sysconfig/network-scripts/ifcfg-eth0
TYPE=Ethernet
DEVICE=eth0
HWADDR=4c:00:10:ac:61:e0
BOOTPROTO=none
ONBOOT=yes
USERCTL=no
IPV6INIT=no
PEERDNS=yes
MASTER=bond0
SLAVE=yes

$ /sbin/ifconfig
 
bond0Link encap:EthernetHwaddr 00:C0:F0:1F:37:B4
inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:255.255.252.0
UP BROADCAST RUNNING MASTER MULTICAST MTU:1500  Metric:1
RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
collisions:0 txqueuelen:0
 
eth0Link encap:EthernetHwaddr 00:C0:F0:1F:37:B4
inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:255.255.252.0
UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500  Metric:1
RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
collisions:0 txqueuelen:100
Interrupt:10 Base address:0x1080
 
eth1Link encap:EthernetHwaddr 00:C0:F0:1F:37:B4
inet addr:XXX.XXX.XXX.YYY Bcast:XXX.XXX.XXX.255 Mask:255.255.252.0
UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500  Metric:1
RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
Interrupt:9 Base address:0x1400

The Lustre software uses the IP address of the bonded interfaces and requires no special configuration. The bonded interface is treated as a regular TCP/IP interface. If needed, specify bond0 using the Lustre networks parameter in /etc/modprobe.

options lnet networks=tcp(bond0)

We recommend the following bonding references:

You can install the Lustre software from downloaded packages (RPMs) or directly from the source code. This chapter describes how to install the Lustre RPM packages. Instructions to install from source code are beyond the scope of this document, and can be found elsewhere online.

The Lustre RPM packages are tested on current versions of Linux enterprise distributions at the time they are created. See the release notes for each version for specific details.

To install the Lustre software from RPMs, complete the steps below.

To configure LNet, go to Chapter 9, Configuring Lustre Networking (LNet). If default settings will be used for LNet, go to Chapter 10, Configuring a Lustre File System.

LNet kernel module (lnet) parameters specify how LNet is to be configured to work with Lustre, including which NICs will be configured to work with Lustre and the routing to be used with Lustre.

Parameters for LNet can be specified in the /etc/modprobe.d/lustre.conf file. In some cases the parameters may have been stored in /etc/modprobe.conf, but this has been deprecated since before RHEL5 and SLES10, and having a separate /etc/modprobe.d/lustre.conf file simplifies administration and distribution of the Lustre networking configuration. This file contains one or more entries with the syntax:

options lnet parameter=value

To specify the network interfaces that are to be used for Lustre, set either the networks parameter or the ip2nets parameter (only one of these parameters can be used at a time):

See Section 9.3, “Setting the LNet Module networks Parameter” and Section 9.4, “Setting the LNet Module ip2nets Parameter” for more details.

To set up routing between networks, use:

See Section 9.5, “Setting the LNet Module routes Parameter” for more details.

A router checker can be configured to enable Lustre nodes to detect router health status, avoid routers that appear dead, and reuse those that restore service after failures. See Section 9.7, “Configuring the Router Checker” for more details.

For a complete reference to the LNet module parameters, see Chapter 37, Configuration Files and Module ParametersLNet Options.

network_id@network_type

10.67.73.200@tcp0
10.67.75.100@o2ib

lctl list_nids

lctl which_nid MDS_NID

If a node has more than one network interface, you'll typically want to dedicate a specific interface to Lustre. You can do this by including an entry in the lustre.conf file on the node that sets the LNet module networks parameter:

options lnet networks=comma-separated list of
    networks

This example specifies that a Lustre node will use a TCP/IP interface and an InfiniBand interface:

options lnet networks=tcp0(eth0),o2ib(ib0)

This example specifies that the Lustre node will use the TCP/IP interface eth1:

options lnet networks=tcp0(eth1)

Depending on the network design, it may be necessary to specify explicit interfaces. To explicitly specify that interface eth2 be used for network tcp0 and eth3 be used for tcp1 , use this entry:

options lnet networks=tcp0(eth2),tcp1(eth3)

When more than one interface is available during the network setup, Lustre chooses the best route based on the hop count. Once the network connection is established, Lustre expects the network to stay connected. In a Lustre network, connections do not fail over to another interface, even if multiple interfaces are available on the same node.

options lnet networks=tcp0(eth0),tcp1(eth1),o2ib

options lnet networks=o2ib

The ip2nets option is typically used when a single, universal lustre.conf file is run on all servers and clients. Each node identifies the locally available networks based on the listed IP address patterns that match the node's local IP addresses.

Note that the IP address patterns listed in the ip2nets option are only used to identify the networks that an individual node should instantiate. They are not used by LNet for any other communications purpose.

For the example below, the nodes in the network have these IP addresses:

The following entry is placed in the lustre.conf file on each server and client:

options lnet 'ip2nets="tcp0(eth0) 192.168.0.[2,4]; \
tcp0 192.168.0.*; o2ib0 132.6.[1-3].[2-8/2]"'

Each entry in ip2nets is referred to as a 'rule'.

The order of LNet entries is important when configuring servers. If a server node can be reached using more than one network, the first network specified in lustre.conf will be used.

Because svr1 and svr2 match the first rule, LNet uses eth0 for tcp0 on those machines. (Although svr1 and svr2 also match the second rule, the first matching rule for a particular network is used).

The [2-8/2] format indicates a range of 2-8 stepped by 2; that is 2,4,6,8. Thus, the clients at 132.6.3.5 will not find a matching o2ib network.

The LNet module routes parameter is used to identify routers in a Lustre configuration. These parameters are set in modprobe.conf on each Lustre node.

Routes are typically set to connect to segregated subnetworks or to cross connect two different types of networks such as tcp and o2ib

The LNet routes parameter specifies a colon-separated list of router definitions. Each route is defined as a network number, followed by a list of routers:

routes=net_type router_NID(s)

This example specifies bi-directional routing in which TCP clients can reach Lustre resources on the IB networks and IB servers can access the TCP networks:

options lnet 'ip2nets="tcp0 192.168.0.*; \
  o2ib0(ib0) 132.6.1.[1-128]"' 'routes="tcp0   132.6.1.[1-8]@o2ib0; \
  o2ib0 192.16.8.0.[1-8]@tcp0"'

All LNet routers that bridge two networks are equivalent. They are not configured as primary or secondary, and the load is balanced across all available routers.

The number of LNet routers is not limited. Enough routers should be used to handle the required file serving bandwidth plus a 25 percent margin for headroom.

lnet networks="tcp" routes="o2ib0 192.168.0.[1-8]@tcp0"

lnet networks="tcp o2ib" forwarding=enabled 

lnet networks="o2ib0" routes="tcp0 132.6.1.[1-8]@o2ib0" 

modprobe lnet
lctl network configure

After configuring Lustre Networking, it is highly recommended that you test your LNet configuration using the LNet Self-Test provided with the Lustre software. For more information about using LNet Self-Test, see Chapter 26, Testing Lustre Network Performance (LNet Self-Test).

In a Lustre configuration in which different types of networks, such as a TCP/IP network and an Infiniband network, are connected by routers, a router checker can be run on the clients and servers in the routed configuration to monitor the status of the routers. In a multi-hop routing configuration, router checkers can be configured on routers to monitor the health of their next-hop routers.

A router checker is configured by setting LNet parameters in lustre.conf by including an entry in this form:

options lnet
    router_checker_parameter=value

The router checker parameters are:

The router checker obtains the following information from each router:

If the router checker does not get a reply message from the router within router_ping_timeout seconds, it considers the router to be down.

If a router is marked 'up' and responds to a ping, the timeout is reset.

If 100 packets have been sent successfully through a router, the sent-packets counter for that router will have a value of 100.

For the networks, ip2nets, and routes options, follow these best practices to avoid configuration errors.

options
      lnet'networks="tcp0,elan0"'
      'routes="tcp [2,10]@elan0"'

lnet: Unknown parameter 'networks'

options lnet ip2nets="pt10 192.168.0.[89,93]; # comment
      with semicolon BEFORE comment \ pt11 192.168.0.[92,96];

options lnet ip2nets="pt10 192.168.0.[89,93] \
# comment with semicolon AFTER comment; \
pt11 192.168.0.[92,96] # comment

A Lustre file system can be set up in a variety of configurations by using the administrative utilities provided with the Lustre software. The procedure below shows how to configure a simple Lustre file system consisting of a combined MGS/MDS, one OSS with two OSTs, and a client. For an overview of the entire Lustre installation procedure, see Chapter 4, Installation Overview.

This configuration procedure assumes you have completed the following:

The following optional steps should also be completed, if needed, before the Lustre software is configured:

For information about configuring LNet, see Chapter 9, Configuring Lustre Networking (LNet). For information about testing LNet, see Chapter 26, Testing Lustre Network Performance (LNet Self-Test).

To configure a simple Lustre file system, complete these steps:

This section describes how to scale the Lustre file system or make configuration changes using the Lustre configuration utilities.

The Lustre software provides failover mechanisms only at the layer of the Lustre file system. No failover functionality is provided for system-level components such as failing hardware or applications, or even for the entire failure of a node, as would typically be provided in a complete failover solution. Failover functionality such as node monitoring, failure detection, and resource fencing must be provided by external HA software, such as PowerMan or the open source Corosync and Pacemaker packages provided by Linux operating system vendors. Corosync provides support for detecting failures, and Pacemaker provides the actions to take once a failure has been detected.

To prepare a Lustre file system to be configured and managed as an HA system by a third-party HA application, each storage target (MGT, MGS, OST) must be associated with a second node to create a failover pair. This configuration information is then communicated by the MGS to a client when the client mounts the file system.

The per-target configuration is relayed to the MGS at mount time. Some rules related to this are:

When the target is formatted using the mkfs.lustre command, the failover service node(s) for the target are designated using the --servicenode option. In the example below, an OST with index 0 in the file system testfs is formatted with two service nodes designated to serve as a failover pair:

mkfs.lustre --reformat --ost --fsname testfs --mgsnode=192.168.10.1@o3ib \  
              --index=0 --servicenode=192.168.10.7@o2ib \
              --servicenode=192.168.10.8@o2ib \  
              /dev/sdb

More than two potential service nodes can be designated for a target. The target can then be mounted on any of the designated service nodes.

When HA is configured on a storage target, the Lustre software enables multi-mount protection (MMP) on that storage target. MMP prevents multiple nodes from simultaneously mounting and thus corrupting the data on the target. For more about MMP, see Chapter 20, Lustre File System Failover and Multiple-Mount Protection.

If the MGT has been formatted with multiple service nodes designated, this information must be conveyed to the Lustre client in the mount command used to mount the file system. In the example below, NIDs for two MGSs that have been designated as service nodes for the MGT are specified in the mount command executed on the client:

mount -t lustre 10.10.120.1@tcp1:10.10.120.2@tcp1:/testfs /lustre/testfs

When a client mounts the file system, the MGS provides configuration information to the client for the MDT(s) and OST(s) in the file system along with the NIDs for all service nodes associated with each target and the service node on which the target is mounted. Later, when the client attempts to access data on a target, it will try the NID for each specified service node until it connects to the target.

Previous to Lustre software release 2.0, the --failnode option to mkfs.lustre was used to designate a failover service node for a primary server for a target. When the --failnode option is used, certain restrictions apply:

For additional information about administering failover features in a Lustre file system, see: