C H A P T E R  13

Lustre Operations

Once you have the Lustre file system up and running, you can use the procedures in this section to perform these basic Lustre administration tasks:


13.1 Mounting by Label

The file system name is limited to 8 characters. We have encoded the file system and target information in the disk label, so you can mount by label. This allows system administrators to move disks around without worrying about issues such as SCSI disk reordering or getting the /dev/device wrong for a shared target. Soon, file system naming will be made as fail-safe as possible. Currently, Linux disk labels are limited to 16 characters. To identify the target within the file system, 8 characters are reserved, leaving 8 characters for the file system name:

<fsname>-MDT0000 or <fsname>-OST0a19

To mount by label, use this command:

$ mount -t lustre -L <file system label> <mount point>

This is an example of mount-by-label:

$ mount -t lustre -L testfs-MDT0000 /mnt/mdt


caution icon Caution - Mount-by-label should NOT be used in a multi-path environment.


Although the file system name is internally limited to 8 characters, you can mount the clients at any mount point, so file system users are not subjected to short names. Here is an example:

mount -t lustre uml1@tcp0:/shortfs /mnt/<long-file_system-name>


13.2 Starting Lustre

The startup order of Lustre components depends on whether you have a combined MGS/MDT or these components are separate.


Note - If an OST is added to a Lustre file system with a combined MGS/MDT, then the startup order changes slightly; the MGS must be started first because the OST needs to write its configuration data to it. In this scenario, the startup order is MGS/MDT, then OSTs, then the clients.


13.3 Mounting a Server

Starting a Lustre server is straightforward and only involves the mount command. Lustre servers can be added to /etc/fstab:

mount -t lustre

The mount command generates output similar to this:

/dev/sda1 on /mnt/test/mdt type lustre (rw)
/dev/sda2 on /mnt/test/ost0 type lustre (rw)
192.168.0.21@tcp:/testfs on /mnt/testfs type lustre (rw)

In this example, the MDT, an OST (ost0) and file system (testfs) are mounted.

LABEL=testfs-MDT0000 /mnt/test/mdt lustre defaults,_netdev,noauto 0 0
LABEL=testfs-OST0000 /mnt/test/ost0 lustre defaults,_netdev,noauto 0 0

In general, it is wise to specify noauto and let your high-availability (HA) package manage when to mount the device. If you are not using failover, make sure that networking has been started before mounting a Lustre server. RedHat, SuSE, Debian (and perhaps others) use the _netdev flag to ensure that these disks are mounted after the network is up.

We are mounting by disk label here--the label of a device can be read with e2label. The label of a newly-formatted Lustre server ends in FFFF, meaning that it has yet to be assigned. The assignment takes place when the server is first started, and the disk label is updated.


caution icon Caution - Do not do this when the client and OSS are on the same node, as memory pressure between the client and OSS can lead to deadlocks.


caution icon Caution - Mount-by-label should NOT be used in a multi-path environment.


13.4 Unmounting a Server

To stop a Lustre server, use the umount <mount point> command.

For example, to stop ost0 on mount point /mnt/test, run:

$ umount /mnt/test

Gracefully stopping a server with the umount command preserves the state of the connected clients. The next time the server is started, it waits for clients to reconnect, and then goes through the recovery procedure.

If the force (-f) flag is used, then the server evicts all clients and stops WITHOUT recovery. Upon restart, the server does not wait for recovery. Any currently connected clients receive I/O errors until they reconnect.


Note - If you are using loopback devices, use the -d flag. This flag cleans up loop devices and can always be safely specified.


13.5 Specifying Failout/Failover Mode for OSTs

Lustre uses two modes, failout and failover, to handle an OST that has become unreachable because it fails, is taken off the network, is unmounted, etc.

By default, the Lustre file system uses failover mode for OSTs. To specify failout mode instead, run this command:

$ mkfs.lustre --fsname=<fsname> --ost --mgsnode=<MGS node NID> --param="failover.mode=failout" <block device name>

In this example, failout mode is specified for the OSTs on MGS uml1, file system testfs.

$ mkfs.lustre --fsname=testfs --ost --mgsnode=uml1 --param="failover.mode=failout" /dev/sdb 


caution icon Caution - Before running this command, unmount all OSTs that will be affected by the change in the failover/failout mode.



Note - After initial file system configuration, use the tunefs.lustre utility to change the failover/failout mode. For example, to set the failout mode, run:

$ tunefs.lustre --param failover.mode=failout <OST partition>


13.6 Handling Degraded OST RAID Arrays

Lustre includes functionality that notifies Lustre if an external RAID array has degraded performance (resulting in reduced overall file system performance), either because a disk has failed and not been replaced, or because a disk was replaced and is undergoing a rebuild. To avoid a global performance slowdown due to a degraded OST, the MDS can avoid the OST for new object allocation if it is notified of the degraded state.

A parameter for each OST, called degraded, specifies whether the OST is running in degraded mode or not.

To mark the OST as degraded, use:

lctl set_param obdfilter.{OST_name}.degraded=1

To mark that the OST is back in normal operation, use:

lctl set_param obdfilter.{OST_name}.degraded=0

To determine if OSTs are currently in degraded mode, use:

lctl get_param obdfilter.*.degraded

If the OST is remounted due to a reboot or other condition, the flag resets to 0.

It is recommended that this be implemented by an automated script that monitors the status of individual RAID devices.


13.7 Running Multiple Lustre File Systems

There may be situations in which you want to run multiple file systems. This is doable, as long as you follow specific naming conventions.

By default, the mkfs.lustre command creates a file system named lustre. To specify a different file system name (limited to 8 characters), run this command:

mkfs.lustre --fsname=<new file system name>


Note - The MDT, OSTs and clients in the new file system must share the same name (prepended to the device name). For example, for a new file system named foo, the MDT and two OSTs would be named foo-MDT0000, foo-OST0000, and foo-OST0001.

To mount a client on the file system, run:

mount -t lustre mgsnode:/<new fsname> <mountpoint>

For example, to mount a client on file system foo at mount point /mnt/lustre1, run:

mount -t lustre mgsnode:/foo /mnt/lustre1

Note - If a client(s) will be mounted on several file systems, add the following line to /etc/xattr.conf file to avoid problems when files are moved between the file systems: lustre.* skip



Note - The MGS is universal; there is only one MGS per Lustre installation, not per file system.



Note - There is only one file system per MDT. Therefore, specify --mdt --mgs on one file system and --mdt --mgsnode=<MGS node NID> on the other file systems.

A Lustre installation with two file systems (foo and bar) could look like this, where the MGS node is mgsnode@tcp0 and the mount points are /mnt/lustre1 and /mnt/lustre2.

mgsnode# mkfs.lustre --mgs /mnt/lustre1
mdtfoonode# mkfs.lustre --fsname=foo --mdt --mgsnode=mgsnode@tcp0 /mnt/lustre1
ossfoonode# mkfs.lustre --fsname=foo --ost --mgsnode=mgsnode@tcp0 /mnt/lustre1
ossfoonode# mkfs.lustre --fsname=foo --ost --mgsnode=mgsnode@tcp0 /mnt/lustre2
mdtbarnode# mkfs.lustre --fsname=bar --mdt --mgsnode=mgsnode@tcp0 /mnt/lustre1
ossbarnode# mkfs.lustre --fsname=bar --ost --mgsnode=mgsnode@tcp0 /mnt/lustre1
ossbarnode# mkfs.lustre --fsname=bar --ost --mgsnode=mgsnode@tcp0 /mnt/lustre2

To mount a client on file system foo at mount point /mnt/lustre1, run:

mount -t lustre mgsnode@tcp0:/foo /mnt/lustre1

To mount a client on file system bar at mount point /mnt/lustre2, run:

mount -t lustre mgsnode@tcp0:/bar /mnt/lustre2


13.8 Setting and Retrieving Lustre Parameters

Several options are available for setting parameters in Lustre:

13.8.1 Setting Parameters with mkfs.lustre

When the file system is created, parameters can simply be added as a --param option to the mkfs.lustre command. For example:

$ mkfs.lustre --mdt --param="sys.timeout=50" /dev/sda

For more details about creating a file system,see Chapter 10: Configuring Lustre. For more details about mkfs.lustre, see Chapter 36: System Configuration Utilities.

13.8.2 Setting Parameters with tunefs.lustre

If a server (OSS or MDS) is stopped, parameters can be added using the --param option to the tunefs.lustre command. For example:

$ tunefs.lustre --param="failover.node=192.168.0.13@tcp0" /dev/sda

With tunefs.lustre, parameters are "additive" -- new parameters are specified in addition to old parameters, they do not replace them. To erase all old tunefs.lustre parameters and just use newly-specified parameters, run:

$ tunefs.lustre --erase-params --param=<new parameters> 

The tunefs.lustre command can be used to set any parameter settable in a /proc/fs/lustre file and that has its own OBD device, so it can be specified as <obd|fsname>.<obdtype>.<proc_file_name>=<value>. For example:

$ tunefs.lustre --param mdt.group_upcall=NONE /dev/sda1

For more details about tunefs.lustre, see Chapter 36: System Configuration Utilities.

13.8.3 Setting Parameters with lctl

When the file system is running, the lctl command can be used to set parameters (temporary or permanent) and report current parameter values. Temporary parameters are active as long as the server or client is not shut down. Permanent parameters live through server and client reboots.


Note - The lctl list_param command enables users to list all parameters that can be set. See Listing Parameters.

For more details about the lctl command, see the examples in the sections below and Chapter 36: System Configuration Utilities.

13.8.3.1 Setting Temporary Parameters

Use lctl set_param to set temporary parameters on the node where it is run. These parameters map to items in /proc/{fs,sys}/{lnet,lustre}. The lctl set_param command uses this syntax:

lctl set_param [-n] <obdtype>.<obdname>.<proc_file_name>=<value>

For example:

# lctl set_param osc.*.max_dirty_mb=1024
osc.myth-OST0000-osc.max_dirty_mb=32 
osc.myth-OST0001-osc.max_dirty_mb=32 
osc.myth-OST0002-osc.max_dirty_mb=32 
osc.myth-OST0003-osc.max_dirty_mb=32 
osc.myth-OST0004-osc.max_dirty_mb=32

13.8.3.2 Setting Permanent Parameters

Use the lctl conf_param command to set permanent parameters. In general, the lctl conf_param command can be used to specify any parameter settable in a /proc/fs/lustre file, with its own OBD device. The lctl conf_param command uses this syntax (same as the mkfs.lustre and tunefs.lustre commands):

<obd|fsname>.<obdtype>.<proc_file_name>=<value>) 

Here are a few examples of lctl conf_param commands:

$ mgs> lctl conf_param testfs-MDT0000.sys.timeout=40
$ lctl conf_param testfs-MDT0000.mdt.group_upcall=NONE 
$ lctl conf_param testfs.llite.max_read_ahead_mb=16 
$ lctl conf_param testfs-MDT0000.lov.stripesize=2M 
$ lctl conf_param testfs-OST0000.osc.max_dirty_mb=29.15 
$ lctl conf_param testfs-OST0000.ost.client_cache_seconds=15 
$ lctl conf_param testfs.sys.timeout=40 

caution icon Caution - Parameters specified with the lctl conf_param command are set permanently in the file system’s configuration file on the MGS.

13.8.3.3 Listing Parameters

To list Lustre or LNET parameters that are available to set, use the lctl list_param command. For example:

lctl list_param [-FR] <obdtype>.<obdname>

The following arguments are available for the lctl list_param command.

-F Add '/', '@' or '=' for directories, symlinks and writeable files, respectively

-R Recursively lists all parameters under the specified path

For example:

$ lctl list_param obdfilter.lustre-OST0000 

13.8.3.4 Reporting Current Parameter Values

To report current Lustre parameter values, use the lctl get_param command with this syntax:

lctl get_param [-n] <obdtype>.<obdname>.<proc_file_name>

This example reports data on RPC service times.

$ lctl get_param -n ost.*.ost_io.timeouts 
service : cur 1 worst 30 (at 1257150393, 85d23h58m54s ago) 1 1 1 1 

This example reports the number of inodes available on each OST.

# lctl get_param osc.*.filesfree
osc.myth-OST0000-osc-ffff88006dd20000.filesfree=217623 
osc.myth-OST0001-osc-ffff88006dd20000.filesfree=5075042 
osc.myth-OST0002-osc-ffff88006dd20000.filesfree=3762034 
osc.myth-OST0003-osc-ffff88006dd20000.filesfree=91052 
osc.myth-OST0004-osc-ffff88006dd20000.filesfree=129651


13.9 Specifying NIDs and Failover

If a node has multiple network interfaces, it may have multiple NIDs. When a node is specified, all of its NIDs must be listed, delimited by commas (,) so other nodes can choose the NID that is appropriate for their network interfaces. When failover nodes are specified, they are delimited by a colon (:) or by repeating a keyword (--mgsnode= or --failnode=). To obtain all NIDs from a node (while LNET is running), run:

lctl list_nids

This displays the server's NIDs (networks configured to work with Lustre).

This example has a combined MGS/MDT failover pair on uml1 and uml2, and a OST failover pair on uml3 and uml4. There are corresponding Elan addresses on uml1 and uml2.

uml1> mkfs.lustre --fsname=testfs --mdt --mgs --failnode=uml2,2@elan /dev/sda1
uml1> mount -t lustre /dev/sda1 /mnt/test/mdt
uml3> mkfs.lustre --fsname=testfs --ost --failnode=uml4 --mgsnode=uml1,1@elan --mgsnode=uml2,2@elan /dev/sdb
uml3> mount -t lustre /dev/sdb /mnt/test/ost0
client> mount -t lustre uml1,1@elan:uml2,2@elan:/testfs /mnt/testfs
uml1> umount /mnt/mdt
uml2> mount -t lustre /dev/sda1 /mnt/test/mdt
uml2> cat /proc/fs/lustre/mds/testfs-MDT0000/recovery_status

Where multiple NIDs are specified, comma-separation (for example, uml2,2@elan) means that the two NIDs refer to the same host, and that Lustre needs to choose the "best" one for communication. Colon-separation (for example, uml1:uml2) means that the two NIDs refer to two different hosts, and should be treated as failover locations (Lustre tries the first one, and if that fails, it tries the second one.)



Note - If you have an MGS or MDT configured for failover, perform these steps:

1. On the OST, list the NIDs of all MGS nodes at mkfs time.

OST# mkfs.lustre --fsname sunfs --ost --mgsnode=10.0.0.1
--mgsnode=10.0.0.2 /dev/{device}

2. On the client, mount the file system.

client# mount -t lustre 10.0.0.1:10.0.0.2:/sunfs /cfs/client/



13.10 Erasing a File System

If you want to erase a file system, run this command on your targets:

$ "mkfs.lustre -reformat"

If you are using a separate MGS and want to keep other file systems defined on that MGS, then set the writeconf flag on the MDT for that file system. The writeconf flag causes the configuration logs to be erased; they are regenerated the next time the servers start.

To set the writeconf flag on the MDT:

1. Unmount all clients/servers using this file system, run:

$ umount /mnt/lustre

2. Erase the file system and, presumably, replace it with another file system, run:

$ mkfs.lustre -reformat --fsname spfs --mdt --mgs /dev/sda

3. If you have a separate MGS (that you do not want to reformat), then add the "writeconf" flag to mkfs.lustre on the MDT, run:

$ mkfs.lustre --reformat --writeconf -fsname spfs --mdt \ --mgs /dev/sda

Note - If you have a combined MGS/MDT, reformatting the MDT reformats the MGS as well, causing all configuration information to be lost; you can start building your new file system. Nothing needs to be done with old disks that will not be part of the new file system, just do not mount them.


13.11 Reclaiming Reserved Disk Space

All current Lustre installations run the ldiskfs file system internally on service nodes. By default, ldiskfs reserves 5% of the disk space for the root user. In order to reclaim this space, run the following command on your OSSs:

tune2fs [-m reserved_blocks_percent] [device]

You do not need to shut down Lustre before running this command or restart it afterwards.


13.12 Replacing an Existing OST or MDS

To copy the contents of an existing OST to a new OST (or an old MDS to a new MDS), use one of these methods:

For example:

mount -t ldiskfs /dev/old /mnt/ost_old
mount -t ldiskfs /dev/new /mnt/ost_new
rsync -aSv /mnt/ost_old/ /mnt/ost_new
# note trailing slash on ost_old/
rsync -aSvz /mnt/ost_old/ new_ost_node:/mnt/ost_new
cd /mnt/mds_old; getfattr -R -e base64 -d . > /tmp/mdsea; \<copy all MDS files as above>; cd /mnt/mds_new; setfattr \--restore=/tmp/mdsea


13.13 Identifying To Which Lustre File an OST Object Belongs

Use this procedure to identify the file containing a given object on a given OST.

1. On the OST (as root), run debugfs to display the file identifier (FID) of the file associated with the object.

For example, if the object is 34976 on /dev/lustre/ost_test2, the debug command is:

# debugfs -c -R "stat /O/0/d$((34976 %32))/34976" /dev/lustre/ost_test2 

The command output is:

debugfs 1.41.5.sun2 (23-Apr-2009)
/dev/lustre/ost_test2: catastrophic mode - not reading inode or group bitmaps 
Inode: 352365   Type: regular    Mode:  0666   Flags: 0x80000
Generation: 1574463214    Version: 0xea020000:00000000
User:   500   Group:   500   Size: 260096
File ACL: 0    Directory ACL: 0
Links: 1   Blockcount: 512
Fragment:  Address: 0    Number: 0    Size: 0
ctime: 0x4a216b48:00000000 -- Sat May 30 13:22:16 2009
atime: 0x4a216b48:00000000 -- Sat May 30 13:22:16 2009
mtime: 0x4a216b48:00000000 -- Sat May 30 13:22:16 2009
crtime: 0x4a216b3c:975870dc -- Sat May 30 13:22:04 2009
Size of extra inode fields: 24
Extended attributes stored in inode body: 
fid = "e2 00 11 00 00 00 00 00 25 43 c1 87 00 00 00 00 a0 88 00 00 00 00 00 00 00 00 00 00 00 00 00 00 " (32)
BLOCKS:
(0-63):47968-48031
TOTAL: 64

2. Note the FID’s EA and apply it to the osd_inode_id mapping.

In this example, the FID’s EA is:

e2001100000000002543c18700000000a0880000000000000000000000000000
struct osd_inode_id { 
__u64 oii_ino; /* inode number */ 
__u32 oii_gen; /* inode generation */ 
__u32 oii_pad; /* alignment padding */ 
};

After swapping, you get an inode number of 0x001100e2 and generation of 0.

3. On the MDT (as root), use debugfs to find the file associated with the inode.

# debugfs -c -R "ncheck 0x001100e2" /dev/lustre/mdt_test 

Here is the command output:

debugfs 1.41.5.sun2 (23-Apr-2009)
/dev/lustre/mdt_test: catastrophic mode - not reading inode or group bitmaps
Inode	Pathname
1114338	/ROOT/brian-laptop-guest/clients/client11/~dmtmp/PWRPNT/ZD16.BMP

The command lists the inode and pathname associated with the object.


Note - Debugfs' ''ncheck'' is a brute-force search that may take a long time to complete.



Note - To find the Lustre file from a disk LBA, follow the steps listed in the document at this URL: http://smartmontools.sourceforge.net/badblockhowto.html.
Then, follow the steps above to resolve the Lustre filename.