Re: why the erasure code pool not support random write?

Lionel Bouton <lionel+ceph@xxxxxxxxxxx> · Tue, 21 Oct 2014 01:40:07 +0200



    Hi,

      
      Le 21/10/2014 01:10, 池信泽 a écrit :

    
      Thanks.
        

           Another reason is the checksum in the attr
          of object used for deep scrub in EC pools should be computed
          when modify the object. When supporting the random write, We
          should caculate the whole object for checksum,
          even if there is a bit modified. If only
          supporting append write, We can get the checksum
          based on the previously checksum and the append
          date which is more quickly. 
          
           Am I
          right?
      
    
    From what I understand, the deep scrub doesn't use a Ceph checksum
    but compares data between OSDs (and probably use a "majority wins"
    rule for repair). If you are using Btrfs it will report an I/O error
    because it uses an internal checksum by default which will force
    Ceph to use other OSDs for repair.

    I'd be glad to be proven wrong on this subject though.

    
    Best regards,

    
    Lionel Bouton

  
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