Re: Reclaim free space on RBD images that use Bluestore?????

Ronny Aasen <ronny+ceph-users@xxxxxxxx> · Tue, 24 Jul 2018 00:13:29 +0200



    On 23.07.2018 22:18, Sean Bolding
      wrote:

    
        I have XenServers that connect via iSCSI to
          Ceph gateway servers that use lrbd and targetcli. On my ceph
          cluster the RBD images I create are used as storage
          repositories in Xenserver for the virtual machine vdisks. 
         
        Whenever I delete a virtual machine,
          XenServer shows that the repository size has decreased. This
          also happens when I mount a virtual drive in Xenserver as a
          virtual drive in a Windows guest. If I delete a large file,
          such as an exported VM, it shows as deleted and space
          available. However; when check in Ceph  using ceph –s or ceph
          df it still shows the space being used.
         
        I checked everywhere and it seems there was
          a reference to it here https://github.com/ceph/ceph/pull/14727
          but not sure if a way to trim or discard freed blocks was ever
          implemented.
         
        The only way I have found is to play
          musical chairs and move the VMs to different repositories and
          then completely remove the old RBD images in ceph. This is not
          exactly easy to do.
         
        Is there a way to reclaim free space on RBD
          images that use Bluestore????? What commands do I use and
          where do I use this from? If such command exist do I run them
          on the ceph cluster or do I run them from XenServer? Please
          help.
         
         
        Sean
         
         
    I am not familiar with Xen, but it does sounds like you have a rbd
    mounted with a filesystem on the xen server.

    in that case it is the same as for other filesystems. Deleted files
    are just deleted in the file allocation table, and the RBD space is
    "reclaimed" when the filesystem zeroes out the now unused blocks. 

    
    in many filesystems you would run the fstrim command to overwrite
    free'd blocks with zeroes, optionally mount the fs with the the
    discard option. 

    in xenserver >6.5 this should be a button in xencenter to reclaim
    freed space. 

    
    kind regards

    Ronny Aasen

  
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