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.

>>> 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



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