Re: Optimum amount of RAM for server

From: Lars (n-o-sp-am-lars_oberg_at_hotmail.com)
Date: 02/23/04 

Date: Mon, 23 Feb 2004 02:49:58 GMT

Thanks guys for the advice!

/ Lars

"Jean-David Beyer" <jdbeyer@exit109.com> wrote in message
news:40393C6D.30506@exit109.com...
> Les Mikesell wrote:
> > "Lars Oberg" <n-o-sp-am-lars_oberg@hotmail.com> wrote in message
> > news:TlXZb.28714$Rn2.23896@newssvr25.news.prodigy.com...
> >
> >> The application is mostly Point-Of-Sale, inventory and accounting
> >> related (over telnet & ssh sessions).
> >>
> >> I know it is really hard to answer this question, but is it likely
> >> (under the above circumstances) to give a noticable performance
> >> boost to double
> >
> > the
> >
> >> RAM (from 2GB to 4GB) in the server?
> >
> >
> > You can get a pretty good idea by observing the machine under a
> > typical load. Run 'top' and look at the free memory and swap usage
> > sections. If you are using a substantial amount of swap space
> > adding RAM will help greatly. If you have a large amount of 'free'
> > memory now, adding more RAM won't help. If neither value is large,
> > more RAM may help but it probably won't be dramatic.
> >
> I find it more fun to run xosview and watch the paging, io rates, etc.
> If you find it is doing more than a page or two per second, you should
> start to consider getting more memory. If you are compute-limited, you
> should consider more or faster CPUs. If you are IO limited, get faster
> peripherals. If none of above and too slow, see if you are seeking too
> much (my current machine does this).
>
> If you seek too much, see if you can get more hard drives. That is what
> I am doing with my new machine (just finished, but not yet smoke tested
> even). I have 4 small 10,000rpm Ultra/320 SCSI hard drives on there. I
> could easily have gotten all that onto a single hard drive, but what I
> wanted was more spindles so that no one drive would have to seek as
> much. If I lay out the data correctly, that is. I can tell my present
> system is seek-limited (though not memory thrashing) because the job
> runs too slowly but is no where near consuming all the CPU time, but it
> is not transferring to disk anywhere near its maximum measured transfer
> rate either. One job takes about 9 hours, runs the CPUs around 5% each,
> transfers only about 1 megabyte/sec to disk even though the disks are
> considerably faster (this is on my current, not my new faster, machine):
>
> /dev/sda:
> geometry = 8759/64/32, sectors = 17938986, start = 0
> Timing buffer-cache reads: 128 MB in 1.04 seconds =123.08 MB/sec
> Timing buffered disk reads: 64 MB in 2.61 seconds = 24.52 MB/sec
>
> /dev/sdb:
> geometry = 8759/64/32, sectors = 17938986, start = 0
> Timing buffer-cache reads: 128 MB in 1.17 seconds =109.40 MB/sec
> Timing buffered disk reads: 64 MB in 2.60 seconds = 24.62 MB/sec
> valinux:root[/home/jdbeyer]#
>
> So if it is not waiting for CPU time (two 550MHz Pentium IIIs), not
> thrashing memory (512MBytes), not transferring data to or from the
> hardrives very fast (4% of capacity), what is it waiting for? Easy, just
> listen to the machine. It seeks so fast and so often (when running that
> job) that you cannot hear the individual clicks the drive makes when it
> seeks.
>
>
> If you do not have xosview and do not want to bother getting it
> (requires X Window System), vmstat will get you the same kind of data,
> but the presentation is not as fun to watch.
>
>
>
> --
> .~. Jean-David Beyer Registered Linux User 85642.
> /V\ Registered Machine 73926.
> /( )\ Shrewsbury, New Jersey http://counter.li.org
> ^^-^^ 6:15pm up 47 days, 5:36, 4 users, load average: 2.20, 2.49, 3.14
>

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