[lustre-discuss] lfs_migrate question

[Ms. Megan Larko]

Greetings to One and All!

I am looking at the lfs_migrate command to move files among OST's in a file
system.
In "Lustre Software Release 2.x Operations Manual" Section 33.2.2
Description of lfs_migrate it indicates that "Because lfs_migrate is not
closely integrated with the MDS, it cannot determine whether a file is
currently open and/or in-use by other applications or nodes.  This makes it
UNSAFE (capitalized in Manual) for use on files that might be modified by
other applications, since the migrated file is only a copy of the current
file.  This results in the old file becoming an open-unlinked file and any
modifications to that file are lost."

All of the lfs_migrate examples show the command being run on an
active/mounted Lustre file system.  Is there any way in which one knows
whether a rebalanced/migrated file was in-use at the time of migration (or
that it was not in-use at the time of migration)?  On a mounted Lustre FS,
is it necessary to make the file system or directories therein read-only
for the migration activity?  Would this trait of lfs_migrate being unable
to determine whether the file scheduled to be migrated is or is not in-use
pose an issue if new OST's are added to the file system and lfs_migrate
command is issued (rather than wait for Lustre to re-balance the load over
new OSTs by attrition, as it were)?

TIA for the clarifications.
Still learning....

megan
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