[GRLUG] swap benchmarking

Michael Mol mikemol at gmail.com
Mon Feb 19 00:08:26 EST 2007

On 2/18/07, Tim Schmidt <timschmidt at gmail.com> wrote:
> On 2/18/07, Michael Mol <mikemol at gmail.com> wrote:
> > Does anyone know of a tool useful for benchmarking swap performance?
> > I'd like to play around with using a USB flash device for swap, to see
> > how it could improve system performance in systems without gobs of
> > RAM. (Indeed, if the performance gain is great enough, it could delay,
> > or even obviate, the need to upgrade system memory in systems where
> > such upgrades are expensive and bandwidth requirements aren't great.)
> Eh...  _most_ USB flash drives read and write at ~10Mb/s max.
> Admittedly, they seek much faster than disks.  However, that 10Mb/s
> isn't going to add much to the ~50Mb/s most modern SATA disks can
> already sustain.  Certainly nothing I'd call noticeable under heavy
> enough swapping to need it.

My expectation is that the seek time benefit will outweight the loss
in throughput, as swap activity is largely random-access.  But I don't
know...that's why I'm looking for a way to benchmark it.

> Ram is reasonably inexpensive, light-weight software is Free, and USB
> flash drives are way too useful to be wasting as swap.

1GB of flash is much cheaper (Computer Club sells 1GB drives for $25)
than 1GB of RAM.  But then, RAM typically has higher throughput.  For
older systems, especially ones for which ram is no longer sold or is
prohibitively expensive, the trade-off could easily be worth it.  If
it's got a PCI slot, you could add a USB2 expansion card and a couple
gigs of low-latency swap to any old PC--effectively giving the system
more memory than it's physically capable of supporting.

> There are, of course, exceptions - my Netgear WGT634Us have 32Mb ram
> and only USB2 as an expansion bus (although in this case, the USB
> flash drive serves as the disk containing / as well...  so it's not
> really any different than your run of the mill desktop).
> Of course, as flash continues to get larger, faster, and cheaper,
> it'll be replacing disks everywhere - even in desktops...  where we're
> at now is somewhere in the uncomfortable middle.

I look forward to the day when I can get a 20GB flash drive to install
my OS on, with a huge magnetic drive for my /home.

> With flash, MRAM, and about a million other variations of all the ways
> we've figured out how to store a bit, the next 5 - 10 years will be
> very exciting for storage.



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