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

[Craig Sanders <cas@taz.net.au>]

On Thu, Apr 05, 2007 at 02:35:59PM +0200, Matus UHLAR - fantomas wrote:
> > > > 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.
> 
> > On Thu, Apr 05, 2007 at 12:30:10PM +0200, Matus UHLAR - fantomas wrote:
> > > 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?
> 
> On 05.04.07 22:19, Craig Sanders wrote:
> > 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).
> 
> and I'm asking if you are sure that will not slow down your system speed.
> The access to this memory will be slower than access to your main RAM,
> because it's limited with PCI/SATA bus speed. Using that memory as RAM may
> slow down your system.

WTF are you talking about?  do you have some kind of comprehension problem?

we're both saying to put the memory into the system. as system ram.  nothing
to do with SATA or PCI bus speed.



> > > > 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.
> 
> depends on amount of data journalled and speed of the device. Try moving
> journal to floppy if you disagree :)

ok, "ANY device" is a little bit of an exaggeration.  obviously, a floppy
would be no good.

but diminishing returns is a real phenomenon. encountered every day.
it's, unfortunately, as common as muck.


> > > 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).
> 
> I agree, I didn't oppose to this argument.

i think you're looking for trivia to quibble about. and getting it wrong
to boot.

i've got better things to do with my time than indulge you in that
tedious game.


craig

-- 
craig sanders <cas@taz.net.au>

BOFH excuse #393:

Interference from the Van Allen Belt.