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:
I'm in the process of setting up a fileserver running oi_151a. How
can I determine the performance improvement from adding log and cache
devices? I'm using filebench with the fileserver personality. Is
that my best choice? So far, I've tried filebench directly on the
server and also on an NFS client. What statistics should I be
watching?
So, can nobody answer my questions?
http://constantin.glez.de/blog/2011/02/frequently-asked-questions-about-flash-memory-ssds-and-zfs
# How Do I Know if an SSD Will Really Help My Write Performance?
<http://constantin.glez.de/blog/2011/02/frequently-asked-questions-about-flash-memory-ssds-and-zfs#write>
# How Do I Know if an SSD Will Really Help My Read Performance?
<http://constantin.glez.de/blog/2011/02/frequently-asked-questions-about-flash-memory-ssds-and-zfs#read>
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.
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.
I have great performance from a FC target using 3 x SAT2-MV8 and 20 x
2Tb sata disks without an ssd zil.
Mark.
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