Messages in this thread | | | Date | Fri, 25 Mar 2011 12:38:28 +0100 | Subject | Re: Union mounts comparison with overlay file system prototype? | From | Szeredi Miklos <> |
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On Thu, Mar 24, 2011 at 2:43 PM, Ric Wheeler <rwheeler@redhat.com> wrote: > Can one or both of you summarize what we union mounts and overlay do better > or worse? Do we need both or just one?
The semantics are very similar, the differences are in the implementation.
Union mounts:
- whiteout/opaque/fallthrough support in filesystems - whiteout operation is atomic - no dentry and inode duplication - copy up on lookup and readdir - does not support union of two read-only trees - merged directory stored in upper tree
Overlayfs
- whiteout/opaque as xattrs - whiteout operation is not atomic - dentry and inode duplication(*) - only copy up on modification - supports union of two read-only trees - merged directory not cached(**)
(*) it's possible to eliminate inode duplication of non-directories with some VFS modifications (**) caching should be possible to do
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