Overview: http://www.nexenta.com/corp/zfs-education/203-nexentastor-an-introduction-to-zfss-hybrid-storage-pool-
The ZIL: See: https://blogs.oracle.com/realneel/entry/the_zfs_intent_log https://blogs.oracle.com/perrin/entry/the_lumberjack http://nex7.blogspot.com/2013/04/zfs-intent-log.html Accordingly it is actually quite ok to use cheap SSD. Two things to do if doing so however: 1) low latency is key keep this in mind when selecting the prospective SSD to use 2) Mirror and stripe the vdev EG: RAID10 ZIL 4x SSD to safe The L2ARC: https://blogs.oracle.com/brendan/entry/test http://www.zfsbuild.com/2010/04/15/explanation-of-arc-and-l2arc/ Accordingly with the L2ARC it is also ok to use cheap SSD same above to two rules apply. However due to the nature of the cache data a striped vdev of 2 SSD is fine as well. Foregoing details but one can also achieve the same sort of general idea to a point as the above with an external journal with ext4. Also with BTRFS mkfs.btrfs -m raid10 SSD SSD SSD SDD -d raid10 <disk> <disk> <disk> <disk> - Chris -----Original Message----- From: owner-scientific-linux-us...@listserv.fnal.gov [mailto:owner-scientific-linux-us...@listserv.fnal.gov] On Behalf Of Graham Allan Sent: Thursday, July 25, 2013 12:54 PM To: Yasha Karant Cc: scientific-linux-users Subject: Re: Large filesystem recommendation I'm not sure if anyone really knows what the reliability will be, but the hope is obviously that these SLC-type drives should be longer-lasting (and they are in a mirror). Losing the ZIL used to be a fairly fatal event, but that was a long time ago (ZFS v19 or something). I think with current ZFS versions you just lose the performance boost if the dedicated ZIL device fails or goes away. There's a good explanation here: http://www.nexentastor.org/boards/2/topics/6890 Graham On Thu, Jul 25, 2013 at 10:41:50AM -0700, Yasha Karant wrote: > How reliable are the SSDs, including actual non-corrected BER, and > what is the failure rate / interval ? > > If a ZFS log on a SSD fails, what happens? Is the log automagically > recreated on a secondary SSD? Are the drives (spinning and/or SSD) > mirrored? Are primary (non-log) data lost? > > Yasha Karant
