[OpenIndiana-discuss] SSD swap space performance

[Reginald Beardsley]

Order of magnitude I already knew.  I was hoping for measured data.  I'm running Solaris 10 on this particular system.  The OI box is a nettop for Internet access.

I'm concerned w/ occasionally running jobs which exceed physical memory.  At most I can only go up to 24 GB by replacing all the 2 GB DIMMS w/ 4 GB DIMMS. 

However, I'd not considered the problem of pathological paging patterns.  On a long job one might well wear out an SSD in a single run which would not be helpful.  I don't think I want to try to figure out what the paging patterns of a large solver like glpk are.  Particularly because it almost certainly problem and option dependent.

A dedicated pair of small, fast disks for swap is probably the best option. To the best of my knowledge Solaris will still interleave paging among multiple swap partitions on separate drives. This was something I routinely did on my systems for many years.

IIRC two matched drives were almost twice as fast as one. It was essential that the drives have identical performance, otherwise it actually slowed the system down.  I vaguely recall that more than two didn't improve performance, but it was a long time ago.  I may not have had 4 identical drives.

Have Fun!
Reg

--- On Wed, 8/8/12, Jan Owoc <jsowoc at gmail.com> wrote:

> From: Jan Owoc <jsowoc at gmail.com>
> Subject: Re: [OpenIndiana-discuss] SSD swap space performance
> To: "Discussion list for OpenIndiana" <openindiana-discuss at openindiana.org>
> Date: Wednesday, August 8, 2012, 10:39 AM
> On Wed, Aug 8, 2012 at 8:49 AM, Udo
> Grabowski (IMK)
> <udo.grabowski at kit.edu>
> wrote:
> > On 08/08/2012 16:47, Reginald Beardsley wrote:
> >>
> >> Has anyone done any testing on the performance of
> an SSD for swap vs disk?
> >> I'm currently fully populated at 12 GB in my Z400.
> >>
> > That should work, but if you really need a fast SSD
> for
> > regularily swapping, you may should start thinking
> about
> > more memory...
> 
> I haven't done testing on OpenIndiana, but in my experience
> swap on an
> SSD is an order of magnitude faster than swap on HDD. Note
> that, as
> Udo pointed out, this is still an order of magnitude (or
> two) slower
> than additional RAM.
> 
> If your workload is such that you have large chunks of
> memory that can
> be swapped out for extended periods of time, then an SSD
> will do this
> several times faster. However, if you have a program that is
> actively
> using more than the 12GB of RAM you have, you will kill your
> SSD (SSDs
> have a limited number of write cycles - each time you'd run
> the
> program, loads of data would hit the SSD) and won't get
> anywhere near
> the performance of actually having adequate memory.
> 
> Jan
> 
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