> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Dave U.Random > > I am planning to revisit SSD again > when the consumer drives are reliable enough and don't have wear issues. > Right now overall integrity and long service life are more important > than absolute performance on this box, although since I have the integrity > with the ZFS mirror I could add an SSD but I really don't want to deal with > another failure as long as I don't have to. I do want additional performance > if I can afford it, but not at the expense of possible data loss.
Right now, (some) consumer drives are reliable enough and don't have wear issues. Not all drives are created equal, but I'm sure you can find an affordable one. Also, if you have an SSD for cache device, you accelerate reads, and there is absolutely no data risk. In the event of cache device failure, performance degrades back to the "normal" level and everything continues just fine. If you have an unmirrored SSD for log device, you accelerate certain types of writes, and while it's not technically true to say there's no data risk, you can generally say there is essentially no data risk. The real truth is, only in the condition of the SSD going bad, and an ungraceful system crash for some unrelated reason coinciding within 5 sec or 30 sec of each other, then up to 5 sec or 30 sec of sync writes could possibly be lost, but the filesystem will never lose integrity. So really truly, there is essentially no data risk. Acceptable for home use, not acceptable for a bank processing transactions. > I don't know what L2ARC is, but I'll take a look on the net. L2ARC is synonymous with "cache" device. System uses the SSD to cache data from the primary storage pool, for the sake of accelerating reads. > I did hear > about ZIL but don't understand it fully, People often say ZIL when they're really talking about a dedicated ZIL log device. It's not correct to use the terms like that, so please stick with "log device" when talking about a dedicated log device. ZIL is the temporary place where sync writes are stored, until they can be written to their permanent locations on primary storage pool. If you don't have a dedicated log device, the ZIL resides on disk with the primary storage pool. So you're able to accelerate sync writes, if you have a dedicated log device which is faster than the primary storage pool. > but I figured spending 500G on ZIL > would be unwise. You couldn't possibly ever use 500G of ZIL, because the ZIL is required to be flushed to disk at least once every 5sec to 30sec (depending on which build you're running.) Even if you have a 4G dedicated log device, that's more than plenty for most purposes. Normally you add a SSD or something like a DDRDrive for dedicated log. Any device which is really fast, even if it is really small, no problem. As long as it's nonvolatile. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
