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Re: [Linux-cluster] managing GFS corruption on large FS



Patton, Matthew F, CTR, OSD-PA&E wrote:
3. gfs_fsck takes a lot of memory to run, and when it runs out of memory, it will start swapping to disk, and that will slow it down considerably.
    So be sure to run it on a system with lots of memory.
define "lots" please.
If I did the math correctly (and that's a leap) gfs_fsck needs approximately
1GB of memory (plus swap) for every 4TB of file system.
So a 40TB fs requires approximately 10GB of memory plus swap, etc.
I'm looking into ways I can reduce this requirement.
RG Structures of 4G or 8G seem reasonable to me. Granted I don't know what the RG's do and what all is involved in the housekeeping. 256mb structures probably makes sense up to say 1/4TB volumes. <1/2TB would take 512mb structs and <1TB would be 1G structures.  Some quick math and I think you'll see where I'm going with this.
Unfortunately, there's a 2GB size limit for each RG in a GFS fs.  I need to
investigate whether the 2GB restriction is artificial or whether we can get
bigger if we need to.  Right now, my new RHEL5 gfs_mkfs just tries to keep
the number of RGs under 10000 and adjusts the RGs accordingly, up to the
2GB maximum.  I just committed this to the HEAD branch of CVS today.

Regards,

Bob Peterson
Red Hat Cluster Suite


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