Re: btrfs backend with autodefrag mount option

Lionel Bouton <lionel-subscription@xxxxxxxxxxx> · Fri, 30 Jan 2015 19:29:56 +0100



    On 01/30/15 14:24, Luke Kao wrote:

    
          Dear ceph users,
          Has anyone tried to add autodefrag and mount option
            when use btrfs as the osd storage?
          
           
          In some previous discussion that btrfs osd startup becomes
            very slow after used for some time, just thinking about add
            autodefrag will help.
           
          We will add on our test cluster first to see if there is
            any difference.
        
      
    We used autodefrag but it didn't help: performance degrades over
    time. One possibility raised in previous discussions here is that
    BTRFS's autodefrag isn't smart enough when snapshots are heavily
    used as is the case with Ceph OSD by default.

    
    There are some tunings available that we have yet to test :

    filestore btrfs snap
filestore btrfs clone range
filestore journal parallel


    All are enabled by default for BTRFS backends. snap is probably the
    first you might want to disable and check how autodefrag and defrag
    behave. It might be possible to use snap and defrag, BTRFS was quite
    stable for us (but all our OSDs are on systems with at least 72GB
    RAM which have enough CPU power so memory wasn't much of an issue).

    
    Best regards,

    
    Lionel Bouton

  
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