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User interaction with Lustre file systems6–2

6.1 Defining file stripe patterns

Lustre presents a POSIX API as the file system interface; this means that POSIX-conformant applications work

with Lustre.

There are occasions when a user who is creating a file may want to create a file with a defined stripe pattern

on a Lustre file system. This section describes two methods of doing this: the first method uses the

lfs executable (see Section 6.1.1), and the second method uses a C program (see Section 6.1.2).

It is also possible to set the stripe configuration on a subdirectory, so that all of the files created in the

subdirectory will inherit the stripe attributes of the subdirectory in preference to those of the file system. See

Section 6.1.3 for information on how to set the stripe configuration on a subdirectory.

6.1.1 Using the lfs executable

From the command line, the lfs executable can be used to determine information about user files. The

lfs getstripe command displays the striping information about a file and the lfs setstripe

command creates a file with the defined striping pattern. Detailed help on the lfs executable is available

from the lfs help menu.

This example creates a file with a stripe width of 4MB, where the system decides the starting OST service

and the number of stripes. It then shows the settings defined by the system.

The commands in the following example assume that the /mnt/lustre/mydirectory directory exists

and can be written to:

$ lfs setstripe /mnt/lustre/mydirectory/file 4194304 -1 0

$ lfs getstripe /mnt/lustre/mydirectory/file

OBDS:

0: ost1_UUID

1: ost2_UUID

./file

obdidx objid objid group

0 68 0x44 0

1 68 0x44 0

$ lfs find --verbose file

OBDS:

0: ost1_UUID

1: ost2_UUID

./file

lmm_magic: 0x0BD10BD0

lmm_object_gr: 0

lmm_object_id: 0x2c009

lmm_stripe_count: 2

lmm_stripe_size: 4194304

lmm_stripe_pattern: 1

obdidx objid objid group

0 68 0x44 0

1 68 0x44 0

The example output shows that the file resides on a file system that has two OST services, ost1_UUID and

ost2_UUID with OST indices 0 (zero) and 1 respectively. The file has a stripe count of 2 and so resides on

both OST services. The stripe size is 4MB. The additional information is for Lustre internal use.

The stripe size must be a multiple of the largest possible page size on any client node. The largest page size

supported on Lustre client nodes is 64KB (for ia64), so that any stripe size specified must be a multiple of

64KB.

The setstripe command prints the following warning if you attempt to set a file stripe size that does not

conform to this rule:

error: stripe_size must be an even multiple of 65536 bytes.

Note that this rule applies to individual files and not to default file system settings, which are described in

Chapter 5 of the HP StorageWorks Scalable File Share System User Guide.

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