Hi Ed, Thanks for your answers. Seem to make sense, sort of…
On 6 May 2010, at 12:21 , Edward Ned Harvey wrote: >> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- >> boun...@opensolaris.org] On Behalf Of Michael Sullivan >> >> I have a question I cannot seem to find an answer to. > > Google for ZFS Best Practices Guide (on solarisinternals). I know this > answer is there. > My Google is very strong and I have the Best Practices Guide committed to bookmark as well as most of it to memory. While it explains how to implement these, there is no information regarding failure of a device in a striped L2ARC set of SSD's. I have been hard pressed to find this information anywhere, short of testing it myself, but I don't have the necessary hardware in a lab to test correctly. If someone has pointers to references, could you please provide them to chapter and verse, rather than the advice to "Go read the manual." > >> I know if I set up ZIL on SSD and the SSD goes bad, the the ZIL will be >> relocated back to the spool. I'd probably have it mirrored anyway, >> just in case. However you cannot mirror the L2ARC, so... > > Careful. The "log device removal" feature exists, and is present in the > developer builds of opensolaris today. However, it's not included in > opensolars 2009.06, and it's not included in the latest and greatest solaris > 10 yet. Which means, right now, if you lose an unmirrored ZIL (log) device, > your whole pool is lost, unless you're running a developer build of > opensolaris. > I'm running 2009.11 which is the latest OpenSolaris. I should have made that clear, and that I don't intend this to be on Solaris 10 system, and am waiting for the next production build anyway. As you say, it does not exist in 2009.06, this is not the latest production Opensolaris which is 2009.11, and I'd be more interested in its behavior than an older release. I am also well aware of the effect of losing a ZIL device will cause loss of the entire pool. Which is why I would never have a ZIL device unless it was mirrored and on different controllers. >From the information I've been reading about the loss of a ZIL device, it will >be relocated to the storage pool it is assigned to. I'm not sure which >version this is in, but it would be nice if someone could provide the release >number it is included in (and actually works), it would be nice. Also, will >this functionality be included in the mythical 2010.03 release? Also, I'd be interested to know what features along these lines will be available in 2010.03 if it ever sees the light of day. > >> What I want to know, is what happens if one of those SSD's goes bad? >> What happens to the L2ARC? Is it just taken offline, or will it >> continue to perform even with one drive missing? > > In the L2ARC (cache) there is no ability to mirror, because cache device > removal has always been supported. You can't mirror a cache device, because > you don't need it. > > If one of the cache devices fails, no harm is done. That device goes > offline. The rest stay online. > So what you are saying is that if a single device fails in a striped L2ARC VDEV, then the entire VDEV is taken offline and the fallback is to simply use the regular ARC and fetch from the pool whenever there is a cache miss. Or, does what you are saying here mean that if I have a 4 SSD's in a stripe for my L2ARC, and one device fails, the L2ARC will be reconfigured dynamically using the remaining SSD's for L2ARC. It would be good to get an answer to this from someone who has actually tested this or is more intimately familiar with the ZFS code rather than all the speculation I've been getting so far. > >> Sorry, if these questions have been asked before, but I cannot seem to >> find an answer. > > Since you said this twice, I'll answer it twice. ;-) > I think the best advice regarding cache/log device mirroring is in the ZFS > Best Practices Guide. > Been there read that, many, many times. It's an invaluable reference, I agree. Thanks Mike --- Michael Sullivan michael.p.sulli...@me.com http://www.kamiogi.net/ Japan Mobile: +81-80-3202-2599 US Phone: +1-561-283-2034 _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
