Configuring Lustre File Striping

Have asked Torben to suggest subtopics for wiki

Intro...Configure striping to optimize performance ...

http://wiki.lustre.org/index.php/Striping_Guidelines

Cl400_OH - Slides 133-114

Page 13 in Torben's paper

OM Chapter 25 - Striping and IO Options

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Using stripes

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

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, which means “stripe over all available OSTs” by entering:

[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 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