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Re: i-ram vs. tmpfs (was: Re: Mail clustering)

On Thu, Apr 05, 2007 at 12:30:10PM +0200, Matus UHLAR - fantomas wrote:
> > > On Wed, Apr 04, 2007 at 07:10:30PM -0400, Matt Cuttler wrote:
> > > > OTOH, it'd be interesting to see how this i-ram card would perform as
> > > > swap space
> > On Wed, Apr 04, 2007 at 11:50:00PM +0000, Andy Smith wrote:
> > > If you have 4G of RAM to put in an i-RAM then why would you use it
> > > as swap?  If your machine swaps, use the 4G as real RAM!
> On 05.04.07 10:05, Craig Sanders wrote:
> > exactly.
> Are you both sure that the speed of accessing the data thgourh SATA
> interface won't slow down your system more than using it as swap device
> in addition to journals?


we're both saying NOT to use it as a swap device, but to put that 4GB
RAM into the system instead (or as well as, if you need both). but
swapping to a ram-disk is just silly unless your M/B can't take any more

> > BTW, from what i've heard, there isn't much difference between using
> > an I-RAM as an external journal and using any reasonably fast disk
> > drive. i.e. using any external journal device gives you most of the
> > benefit, after that it's diminishing returns. and a new hard disk is a
> > lot cheaper than an I-RAM. about $50 AUD for a brand-new 80GB drive,
> > which is about the smallest drive you can get nowadays.
> That's possible, but it adds some reliability contrary to other devices.
> > i.e. spend $50 on a new SATA drive for the external journal device
> > and get 80-90% of the performance improvement that you would get for
> > spending $500 on a 4GB I-RAM.
> the problem is probably the SATA bus speed... 

no, it's not.  it's diminishing returns.

moving the journal onto another device - ANY other device - gives you
a big benefit. once you've done that, even moving it to a much faster
device doesn't give you anywhere near the same additional benefit.

> but even you say it's faster :)

yes, using an SSD for fs journalling *WILL* be faster than using a
hard-disk. it will also cost a *LOT* more than a hard disk, 10 times
more using my figures above (and a lot more than that if you use a
"real" SSD rather than an I-RAM).

for most people, the small extra additional benefit isn't worth the much
greater cost.

depending, of course, on exactly how much you need a few extra %
performance, and how much money you can afford to throw at it.


craig sanders <cas@taz.net.au>

The longer I am out of office, the more infallible I appear to myself.
		-- Henry Kissinger

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