4 ms·
Under "ZFS Bad" should be listed: - desperately needs defrag, which it does not have If you fill up a ZFS filesystem, even to just 90% full, it will have crip
by rsync 12y ago
Under "ZFS Bad" should be listed:
- desperately needs defrag, which it does not have
If you fill up a ZFS filesystem, even to just 90% full, it will have crippling performance degradation. Further, freeing space to bring it below XX% will sort of solve the problem, but you will get that degradation sooner and sooner (85%, then 80%, etc.) as you refill it.
- bhouston 12y agoYup, ran into this in production. Great way to bring down a database server.
- cbd1984 12y ago> desperately needs defrag, which it does not have OK, this is interesting to me, because it takes me back to the 1990s, when Windows users coming from Windows 95 (who were also Windows 3.11 and MS-DOS users prior to that) would come to Linux and, having been of the Power User variety back in Windows-land, would ask "How do I defrag my disks?" Of course, by then Linux was on ext2 or similar, so the response was "Real filesystems don't need defragging. The kernel keeps track of free space automatically. Don't worry about it." And, generally, it worked pretty well. (Source: I like to fill disks. I've never seen a big slowdown even unto the point of "no space left on medium" errors.) So why does ZFS, a Thoroughly Modern Filesystem by any account, need defragging?
- wbkang 12y agoYou can still have fragmentation problem with ext or ZFS if your file system is near full. This always has been a problem. The problem with FAT was that the fragmentation problem occured earlier than other systems.
- RexRollman 12y agoDefragging can be useful for some file systems. XFS has one.
- makomk 12y agoEven ext4 has an online defragmenter these days.
- aidenn0 12y agoext2 was set by default to disallow non-root writes to disk at something like 90% or 95% full as even it would fragment under typical usage when too full.
- switch007 12y agoWhat causes the performance degradation at sooner and sooner levels of fullness?
- rsync 12y agoFragmentation.
- davidgerard 12y agoBeen bitten by this one in production. We had to reboot the production box to clear it, which was a nontrivial thing to have to do. We expected better of Solaris. (We did get a ZFS dev in the loop, which was pretty cool. This was Solaris 10 in the Sun days.)