Hello,
I had a question about XFS integrity and performing block-level
snapshots.
We currently have a 2TB (but growing soon..) volume mounted by a Linux
host with kernel 2.6.23 over iSCSI from our SAN. Our SAN unit has the
capability to perform block-level snapshots, which is done at regular
intervals.
I know that it is recommended to perform an xfs_freeze before
performing a snapshot. However, the control of the snapshots is
independent from the OS, which currently has no knowledge of their
occurrence. I'm curious as to the repercussions of this. I understand
that in all likelyhood, the integrity of files which are currently
being written will not be preserved. However, even with an xfs_freeze
this is not guaranteed, as an application may require additional disk
transactions to maintain the file in a valid state (it is not
necessarily atomic, depending on the application).
As far as metadata transactions are concerned, the journal should make
these atomic, so there should not be any problem there?
Basically, I'd like to know what is the worst that could happen, and
why an xfs_freeze is necessary in this scenario.
____________
Kamil Kisiel
HPC Systems Engineer, Zymeworks Inc.
201-1401 West Broadway,
Vancouver, BC, V6H 1H6, Canada
Tel: (604) 678-1388 ext. 135
Fax: (604) 737-7077
www.zymeworks.com
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