I did some benchmarking using a standard 7200 RPM disk and a 128MB ramdisk.
The machine was not using any swap, so there was no chance of the ramdisk
accidentally making it to disk.
In short, performance on it sucked. The throughput was about 10% less than
IDE, but seeks/sec were 5-10 times more. However, the CPU was maxed at 100%
during tests to the ramdisk.
Jay
-----Original Message-----
From: Oliver White [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, July 18, 2000 12:27 AM
To: [EMAIL PROTECTED]
Subject: Re: questions about performance and setup
Steve Wolfe wrote:
> > With all of the emails I recieved, I get the impression that I'm going
to
> > I/O bound instead of processor or memory bound. How much disk will be
> > sufficient for the queue? 1GB? More?
>
> It's not so much a matter of disk size (I don't think you'll have a 1
gig
> queue!),
You could quite easily get a 1 Gig queue, even if you don't run into the
obvious problem of temporary loss of network connectivity. Say you've
got 200,000 subscribers and you generate your messages twice as fast
as qmail can send them, then when you've finished generating the
messages you've still got 100,000 in the queue. If the messages are
10Kb each, that's 1 Gb.
> > (I can put 2GB of ram in the box)? Linux has support for making a disk
in
> > memory, putting a filesystem on it and mounting it. Wouldn't this take
> > care of I/O problems?
>
> That's about as good of I/O as you can get, I would imagine. ; ) As
> another author stated, the largest gain would be in writes, but that's
where
> the largest expenditure is anyway. Just make dang, dang sure that your
> machine is NOT going to have any hiccups or lose power while the queue is
> full, or you'll instantly lose it all.
What if you put the 2 Gb RAM in the box, but let Linux use it as a disk
cache?
I'm not sure how the disk caching under Linux works, but if you create a
file
and then delete it before it actually gets written to disk, is there any
disk
activity required?
Sure, the disks will be thrashing away, trying to keep up, but would the I/O
actually block if there was still room in the disk cache?
- Oliver.
