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_loghttps://blogs.oracle.com/perrin/entry/the_lumberjackhttp://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/testhttp://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: [log in to unmask] [mailto:[log in to unmask]] 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
