The intended use is NFS storage to back some VMWare servers running a range of different VM's, including Exchange, Lotus Domino, SQL Server and Oracle. :-) It's a very random workload, and all the research I've done points to mirroring as the better option for providing a better total IOP/s. The server in question is limited in the amount of RAM it can take, so the effectiveness of both the arc and l2arc will be limited somewhat, so I believe mirroring to be lower risk from a performance point of view. But I've got mirrored 25-E's in there for the zil, and an X25-M for arc as well.
Obviously some of this situation is not ideal, nor of my choosing. I'd like to have a newer-faster server in there, and a second JBOD for more drives, and probably another couple of X25-M's. Actually, I'd like to just grab one of the Sun 7000 series and drop that in. :-) The only way I'll get approval for the extra expenditure is to show that the current system is viable in an initial proof of concept limited deployment project, and one of the ways I'm doing that is to ensure I get what I believe to be the best possible performance from my existing hardware - and I think mirroring will do that. Performance was actually more important than capacity, and I wasn't willing to bet in advance on the arc's effectiveness. Actually, I believe the current system will give me the requisite IOP/s without the l2arc, I added the arc because for the cost I considered it silly not to considering the relative cost. For those periods that it is effective, it really makes a difference too! T. ________________________________ From: Tim Cook [mailto:t...@cook.ms] Sent: Wednesday, 26 August 2009 3:48 PM To: Tristan Ball Cc: zfs-discuss@opensolaris.org Subject: Re: [zfs-discuss] Using consumer drives in a zraid2 On Wed, Aug 26, 2009 at 12:27 AM, Tristan Ball <tristan.b...@leica-microsystems.com> wrote: The remaining drive would only have been flagged as dodgy if the bad sectors had been found, hence my comments (and general best practice) about data scrub's being necessary. While I agree it's possibly likely that the enterprise drive would flag errors earlier, I wouldn't necessarily bet on it. Just because a given sector has successfully been read a number of times before doesn't guarantee that it will be read successfully again, and again the enterprise drive doesn't try as hard. In the absence of scrubs, resilvering can be the hardest thing the drive does, and by my experience is likely to show up errors that haven't occurred before. But you make a good point about retrying the resilver until it works, presuming I don't hit a "too many errors, device faulted" condition. :-) I would have liked to go RaidZ2, but performance has dictated mirroring. Physical, Financial and Capacity constraints have conspired together to restrict me to 2 way mirroring rather than 3 way, which would have been my next choice. :-) Regards Tristan (Who is now going to spend the afternoon figuring out how to win lottery by osmosis: http://en.wikipedia.org/wiki/Osmosis :-) ) My suggestion/question/whatever would be: why wouldn't raidz+an SSD arc not meet both financial and performance requirements? It would literally be a first for me. --Tim ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
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