On Fri, 31 Oct 2014, "Peter Ross" <[email protected]> wrote: > The article also mentions some speed issues especially in relation to > databases.
COW filesystems use different blocks on disk every time a file is written to. For a file that is randomly written that leads to massive fragmentation which either kills linear read performance or requires online defragmentation (which hurts performance too). > I would be interested to know what Oracle says to databases on ZFS on > Solaris - and Btrfs on Linux systems (the later not supported by Oracle > yet, I believe, the first I am not sure about) The same performance issues apply to BTRFS and ZFS. The significant difference is that L2ARC and ZIL can mitigate such problems - and possibly give better performance than a traditional filesystem such as XFS on a plain RAID array. > My gut feeling: Use Btrfs for "bread and butter" work and not if you need > 101% reliability. With backups and mirrors and failovers (which may be in > place anyway) you may be fine. If you want good reliability then you need backups and mirrors anyway. > I just do not get my head around why a subvolumes is called subvolume if > it is (according to the FAQ) comparable to a file system - you just can > have many of them in a pool. A subvolume is represented inside BTRFS in much the same way a directory. You can't mount one subvol without operating on the rest of the filesystem, so if a filesystem is corrupted such that it can only be mounted RO then that applies to all subvols. On Fri, 31 Oct 2014, Avi Miller <[email protected]> wrote: > Yeah, COW filesystems in general are not great for DB performance. Or VM > performance. We usually recommend disabling the COW on those files (as the > DB/VM product should do some form of transaction control). I disagree. I think that it's best to have reliability features at every possible level of the stack. If you can afford the performance hit of running a database on ZFS or BTRFS then you should do it. If you are going for an all-Sun environment then the cases where the incremental cost of using COW on ZFS for a database exceed the potential benefits seem likely to be very rare. The vast majority of database installations don't require hardware that is particularly powerful by today's standards. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/ _______________________________________________ luv-main mailing list [email protected] http://lists.luv.asn.au/listinfo/luv-main
