[Lustre-discuss] Direct Snapshots of Lustre Filesystem & MDT size

Nick Jennings | Technical Director nick at creativemotiondesign.com
Fri Apr 17 05:45:59 PDT 2009


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Hello,

 I've got two questions that don't seem to be answered in the Lustre
Operations Manual.

- - The first is recommended MDT size. How big should your MDT partition
be? Does it depend on your estimated eventual size of your Lustre file
system? If so whats the ratio?

- - The next question has to do with backing up a Lustre file system. In
the operations manual, it says that there is significant CPU overhead
when snapshotting the Lustre file system directly. However the
recommended work around is to make a separate LVM file system, copy
important files/directories on it - then take a snapshot of that.

 This kind of skirts the issue for me, ideally I'd like to backup the
entire file system (everything is important). Making a full copy of the
file system on another drive is already a backup in and of itself.
Doesn't this kind of defeat the purpose? I can understand if you only
need a few files backed up, but if you have a 5TB file system, and want
a snapshot of it, it doesn't make much sense to make another 5TB LVM
slice, and copy everything there - then take a snapshot of that.

 The manual doesn't explain how to snapshot the lustre file system
directly. Is it not supported? Would it cost a significant amount of CPU
 cycles just during the snapshotting process, or continuously during the
course of operations, in order to maintain the snapshot?


Thanks for any advice on these issues.
- -Nick


- --
Nick Jennings
Technical Director
Creative Motion Design
www.creativemotiondesign.com
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