[OpenIndiana-discuss] Fileserver performance with log and cache devices?

[Gary Mills]

On Sat, Dec 03, 2011 at 10:45:42AM +1300, Mark wrote:
> On 3/12/2011 9:34 a.m., Per Sjoholm wrote:
> >On 12/02/2011 07:44 PM, Gary Mills wrote:
> >>On Thu, Dec 01, 2011 at 08:59:48AM -0600, Gary Mills wrote:
[...]
> >>>To begin, I'm using a single 1 TB SAS disk on the server, without log
> >>>or cache devices. I intend to add an Intel 311 SSD for the log and
> >>>Intel 320 SSDs for the cache. I'd like to ensure that these improve
> >>>NFS performance. I'd like CIFS and zfs send performance to be
> >>>reasonable as well.
> >
> The simple answer is, they can help, but I doubt you will see much
> improvement with a single disk, since that is the major bottleneck.

I do need three more Seagate ST31000424SS disks.  They were one to a
customer, but now they seem to have disappeared from the market with
no replacement.

> The standard disk i/o performance guidelines like spindle count and
> rpm still apply.
> 
> Read cache is only useful if the same file or data is being read
> multiple times, since the cache needs to be populated.
> 
> For writes, if the server has plenty of memory and a zpool with an
> optimal spindle count is as fast as an ssd, then it won't give as
> much benefit, although it does have the benefit of being
> non-volatile.
> I seem to recall mention that the dedicated zil is only used if it's
> needed.

It's needed for synchronous writes, which will be a bottleneck for
NFS.  That's why I wanted to be certain that my SSD log device
improved performance.

> I have great performance from a FC target using 3 x SAT2-MV8 and 20
> x 2Tb sata disks without an ssd zil.

-- 
-Gary Mills-		-refurb-		-Winnipeg, Manitoba, Canada-