Lustre 1.6 Operations Manual

23.4 Looking at Disk Content
In Lustre, the inodes on the metadata server contain extended attributes (EAs) that
store information about file striping. EAs contain a list of all object IDs and their
locations (that is, the OST that stores them). The lfs tool can be used to obtain this
information for a given file via the getstripe sub-command. Use a corresponding
lfs setstripe command to specify striping attributes for a new file or directory.
The lfs getstripe utility is written in C; it takes a Lustre filename as input and
lists all the objects that form a part of this file. To obtain this information for the file
/mnt/lustre/frog in Lustre filesystem, run:
$ lfs getstripe /mnt/lustre/frog
$
OBDs:
0 : OSC_localhost_UUID
1: OSC_localhost_2_UUID
2: OSC_localhost_3_UUID
obdix
objid
0 17
1 4
The debugfs tool is provided by the e2fsprogs package. It can be used for interactive
debugging of an ext3/ldiskfs filesystem. The debugfs tool can either be used to
check status or modify information in the filesystem. In Lustre, all objects that
belong to a file are stored in an underlying ldiskfs filesystem on the OST's. The
filesystem uses the object IDs as the file names. Once the object IDs are known, the
debugfs tool can be used to obtain the attributes of all objects from different OST's. A
sample run for the /mnt/lustre/frog file used in the example above is shown here:
$ debugfs -c /tmp/ost1
debugfs: cd O
debugfs: cd 0 /* for files in group 0 */
debugfs: cd d
debugfs: stat /* for getattr on object */
debugfs: quit
## Suppose object id is 36, then follow the steps below:
$ debugfs /tmp/ost1
debugfs: cd O
debugfs: cd 0
debugfs: cd d4 /* objid % 32 */
debugfs: stat 36 /* for getattr on obj 4*/
debugfs: dump 36 /tmp/obj.36 /* dump contents of obj 4 */
debugfs: quit
Chapter 23 Lustre Debugging 23-13