Shrinking Support

Revision as of 18:34, 21 December 2008 by Sandeen (talk | contribs) (remove dup bullet point)
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Currently XFS Filesystems can't be shrunk.

To suppor shrinking XFS filesystems a few thinks needs to be implemented, based on a list by Dave Chinner [1]:

  • A way to check space is available for shrink
  • An ioctl or similar interface to prevent new allocations from a given allocation group.
  • A variant of the xfs_reno tool to support moving inodes out of filesystem areas that go away.
  • A variant of the xfs_fsr tool to support moving data out of the filesystem areas that go away.
  • Some way to move out orphan metadata out of the AGs truncated off
  • A transaction to shrink the filesystem.

At that point, we'll got a "working" shrink that will allow shrinking to only 50% of the original size because the log will get in the way. To fix that, we'll need to implement transactions to move the log...

Available pieces

  • A script from Ruben Porras to check if enough free space is available to support shrinking [[2]]
  • A patch from Ruben Porras to allow / disallow allocation from an allocation group [3] plus userspace support for setting / clearing it [4]
  • The xfs_fsr tool in xfsprogs
  • An untested patch from Dave Chinner for a xfs_swap_inodes ioctl that allows to not just defragment extents but moving the whole inode [5] and a patch to xfs_reno to use it from Ruben Porras [6]