On Jan 3, 2013, at 8:38 PM, Geoff Nordli <geo...@gnaa.net> wrote: > Thanks Richard, Happy New Year. > > On 13-01-03 09:45 AM, Richard Elling wrote: >> On Jan 2, 2013, at 8:45 PM, Geoff Nordli <geo...@gnaa.net> wrote: >> >>> I am looking at the performance numbers for the Oracle VDI admin guide. >>> >>> http://docs.oracle.com/html/E26214_02/performance-storage.html >>> >>> From my calculations for 200 desktops running Windows 7 knowledge user (15 >>> iops) with a 30-70 read/write split it comes to 5100 iops. Using 7200 rpm >>> disks the requirement will be 68 disks. >>> >>> This doesn't seem right, because if you are using clones with caching, you >>> should be able to easily satisfy your reads from ARC and L2ARC. As well, >>> Oracle VDI by default caches writes; therefore the writes will be coalesced >>> and there will be no ZIL activity. >> >> All of these IOPS <--> VDI users guidelines are wrong. The problem is that >> the variability of >> response time is too great for a HDD. The only hope we have of getting the >> back-of-the-napkin >> calculations to work is to reduce the variability by using a device that is >> more consistent in its >> response (eg SSDs). > > For sure there is going to be a lot of variability, but it seems we aren't > even close. > > Have you seen any back-of-the-napkin calculations which take into > consideration SSDs for cache usage?
Yes. I've written a white paper on the subject, somewhere on the nexenta.com website (if it is still available). But more current info is presentation at ZFSday. http://www.youtube.com/watch?v=A4yrSfaskwI http://www.slideshare.net/relling >>> >>> Anyone have other guidelines on what they are seeing for iops with vdi? >>> >> >> The successful VDI implementations I've seen have relatively small space >> requirements for >> the performance-critical work. So there are a bunch of companies offering >> SSD-based arrays >> for that market. If you're stuck with HDDs, then effective use of >> snapshots+clones with a few >> GB of RAM and slog can support quite a few desktops. >> -- richard >> > > Yes, I would like to stick with HDDs. > > I am just not quite sure what quite a few desktops mean. > > I thought for sure there would be lots of people around that have done small > deployments using a standard ZFS deployment. ... and large :-) I did 100 desktops with 2 SSDs two years ago. The presentation was given at OpenStorage Summit 2010. I don't think there is a video, though :-(. Fundamentally, people like to use sizing in IOPS, but all IOPS are not created equal. An I/O satisfied by ARC is often limited by network bandwidth constraints whereas an I/O that hits a slow pool is often limited by HDD latency. The two are 5 orders of magnitude different when using HDDs in the pool. -- richard -- richard.ell...@richardelling.com +1-760-896-4422
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