Configuring Lustre File Striping

One of the main factors leading to the high performance of Lustre file systems is the ability to stripe data over multiple OSTs. The stripe count can be set on a file system, directory, or file level. An example showing the use of striping is provided below.

For additional information, see Chapter 25: "Striping and IO Options" in the Lustre Operations Manual

Using Stripes
To see the current stripe size, use the command lfs getstripe [file, dir, fs]. This command will produce output similar to the following:

root@LustreClient01 lustre]# lfs getstripe /mnt/lustre OBDS: 0: lustre-OST0000_UUID ACTIVE 1: lustre-OST0001_UUID ACTIVE 2: lustre-OST0002_UUID ACTIVE 3: lustre-OST0003_UUID ACTIVE 4: lustre-OST0004_UUID ACTIVE 5: lustre-OST0005_UUID ACTIVE /mnt/lustre (Default) stripe_count: 2 stripe_size: 4M stripe_offset: 0

In this example, the default stripe count is 2 (that is, data blocks are striped over two OSTs), the default stripe size is 4 MB (the stripe size can be set in K, M or G), and all writes start from the first OST.

Note: When setting the stripe, the offset is set before the stripe count.

The command to set a new stripe pattern on the file system may look like this:

[root@LustreClient01 lustre]# lfs setstripe /mnt/lustre 4M 0 1

This example command sets the stripe of /mnt/lustre to 4 MB blocks starting at OST0 and spanning over one OST. If a new file is created with these settings, the following results are seen:

[root@LustreClient01 lustre]# dd if=/dev/zero of=/mnt/lustre/test1 bs=10M count=100

root@LustreClient01 lustre]# lfs df -h UUID                 bytes     Used  Available   Use%   Mounted on lustre-MDT0000_UUID    4.4G   214.5M       3.9G     4%   /mnt/lustre[MDT:0] lustre-OST0000_UUID   2.0G     1.1G     830.1M    53%   /mnt/lustre[OST:0] lustre-OST0001_UUID   2.0G    83.3M       1.8G     4%   /mnt/lustre[OST:1] lustre-OST0002_UUID   2.0G    83.3M       1.8G     4%   /mnt/lustre[OST:2] lustre-OST0003_UUID   2.0G    83.3M       1.8G     4%   /mnt/lustre[OST:3] lustre-OST0004_UUID   2.0G    83.3M       1.8G     4%   /mnt/lustre[OST:4] lustre-OST0005_UUID   2.0G    83.3M       1.8G     4%   /mnt/lustre[OST:5]

filesystem summary:  11.8G     1.5G       9.7G    12%   /mnt/lustre

In this example, the entire file was written to the first OST with a very uneven distribution of data blocks.

Continuing with this example, the file is removed and the stripe count is changed to a value of -1 to specify striping over all available OSTs:

[root@LustreClient01 lustre]# lfs setstripe /mnt/lustre 4M 0 -1

Now, when a file is created, the new stripe setting evenly distributes the data over all the available OSTs:

[root@LustreClient01 lustre]# dd if=/dev/zero of=/mnt/lustre/test1 bs=10M count=100 100+0 records in 100+0 records out 1048576000 bytes (1.0 GB) copied, 20.2589 seconds, 51.8 MB/s

[root@LustreClient01 lustre]# lfs df -h UUID                 bytes     Used  Available   Use%   Mounted on lustre-MDT0000_UUID    4.4G   214.5M       3.9G     4%  /mnt/lustre[MDT:0] lustre-OST0000_UUID   2.0G   251.3M       1.6G    12%  /mnt/lustre[OST:0] lustre-OST0001_UUID   2.0G   251.3M       1.6G    12%  /mnt/lustre[OST:1] lustre-OST0002_UUID   2.0G   251.3M       1.6G    12%  /mnt/lustre[OST:2] lustre-OST0003_UUID   2.0G   251.3M       1.6G    12%  /mnt/lustre[OST:3] lustre-OST0004_UUID   2.0G   247.3M       1.6G    12%  /mnt/lustre[OST:4] lustre-OST0005_UUID   2.0G   247.3M       1.6G    12%  /mnt/lustre[OST:5]

filesystem summary:  11.8G     1.5G       9.7G    12%  /mnt/lustre

Determining stripe information for a file
The lfs getstripe command can be used to display information that shows over which OSTs a file is distributed. For example, the output from the following command (showing multiple obdidx entries) indicates that the file test1 is striped over all six active OSTs in the configuration:

[root@LustreClient01 ~]# lfs getstripe /mnt/lustre/test1 OBDS: 0: lustre-OST0000_UUID ACTIVE 1: lustre-OST0001_UUID ACTIVE 2: lustre-OST0002_UUID ACTIVE 3: lustre-OST0003_UUID ACTIVE 4: lustre-OST0004_UUID ACTIVE 5: lustre-OST0005_UUID ACTIVE /mnt/lustre/test1 obdidx     objid     objid      group 0         8       0x8          0 1         4       0x4          0 2         5       0x5          0 3         5       0x5          0 4         4       0x4          0 5         2       0x2          0

In contrast, the output from the following command, which lists just a single obdidx entry, indicates that the file test2 is contained on a single OST:

[root@LustreClient01 ~]# lfs getstripe /mnt/lustre/test_2 OBDS: 0: lustre-OST0000_UUID ACTIVE 1: lustre-OST0001_UUID ACTIVE 2: lustre-OST0002_UUID ACTIVE 3: lustre-OST0003_UUID ACTIVE 4: lustre-OST0004_UUID ACTIVE 5: lustre-OST0005_UUID ACTIVE /mnt/lustre/test_2 obdidx     objid     objid      group 2         8       0x8          0