[K12OSN] Server Tuning
Owen O Donovan
odonovan at bsd.sk.ca
Tue Apr 19 20:07:25 UTC 2005
Have you tried using iostat? You can find it in the sysstat rpm.
iostat <interval in sec>
gives you really great, humanly understandable, data on your disk subsys.
My reading from your description is that a single drive isn't adequate to
keep up with the demands. iostat should show that.
We run up to 60 (usu.30) concurrent smb sessions, about 10 - 20 afpd and
between 100 and 200 nfs sessions concurrently on 866MHz PIII machines w 512MB
RAM. The big difference is that we run software raid 5 for home across 4 or 5
disks. The sw RAID adds some CPU load peaking to 10-15% --easily managed by
the generally low CPU demands on a file server.
I'd suggest another disk or two and sw RAID /home across the bunch.
Owen O'Donovan
Technology Coordinator
Battlefords School Division
--
Open WebMail Project (http://openwebmail.org)
---------- Original Message -----------
From: linuxk12 at mountainlake.k12.mn.us
To: k12osn at redhat.com
Sent: Tue, 19 Apr 2005 11:03:40 -0500
Subject: [K12OSN] Server Tuning
> I have a server that is getting bogged down and am wondering how I
> can tune it for better performance.
>
> Initially when I noticed response times slowing, I used "top" to
> see what was going on. When load averages are over 3.0,
> sometimes 5.0 and greater, response time is very poor. At the
> same time, top reported that the processor was 90% idle or better.
>
> That led me wonder if there was an i/o bottleneck with the processor
> idling while waiting for disk accesses to be completed. I don't know
> how to check for that.
>
> More recently I discovered "vmstat" and have been using that to monitor
> what is going on. Swapping doesn't appear to be a major problem
> ("si" and "so" are usually at zero), so more memory wouldn't help me
> with respect to swapping. Would more memory help for some other reason?
>
> What vmstat did show is that context switching is getting out of hand
> during the times when the server appears overloaded. Typically the
> "cs" numbers are in the 300-500 range when things are humming along
> nicely. But something will push that number into the 1000's then the
> 10,000's and sometimes 100,000s and the box stalls out at that point,
> waiting for the backlog to clear. I typically use "vmstat 5" to
> see five second data.
>
> So, I'm wondering if there is something I can tune to fix this. Are
> there other monitoring tools I can use to show that my tuning is helping
> things? Failing a tuning solution, what do I need to do to ensure that
> a new server has enough power to overcome this problem?
>
> These are the specifics on the server. This is a Dell server running
> RedHat with kernel 2.4.18-3. It is mostly a file server that
> supports NFS, smb and netatalk (AppleTalk) for about 160 computers.
> There are about 80 smb connections and 80 live NFS connections all
> day long of which perhaps a third to half are actively transferring
> data at the same time.
>
> The same server also acts as an ldap database (for the OSX clients) and
> mail server (sendmail, spamassassin, imap). Here is a count of some
> of these processes that are all running at the same time as reported
> by 'ps':
>
> 5 identd
> 5 spamd
> 7 /var/openldap/libexec/slapd
> 8 [kjournald]
> 8 [nfsd]
> 20 imapd --- this looks unusual!
> 22 /usr/sbin/afpd
> 36 smbd
>
> >From /proc/cpuinfo:
>
> vendor_id : GenuineIntel
> cpu family : 6
> model : 11
> model name : Intel(R) Pentium(R) III CPU family 1400MHz
> stepping : 1
> cpu MHz : 1396.496
> cache size : 512 KB
> bogomips : 2785.28
>
> There are two SCSI drives formated as ext3 and the drive that sees
> most of the io is mounted like this:
>
> /dev/sdb1 /home ext3 rw,data=writeback,usrquota 0 0
>
> So obviously I am using user quotas. I don't remember what "writeback"
> is doing for me.
>
> Initially I was looking at performance issues to see if I should upgrade
> to a gigabit ether connection, but with the current performance
> problems, it doesn't appear to be able to fill even a 100Mb pipe.
>
> Any suggestions are welcome. If I need to invest some dollars to fix
> this I will, but I want to spend them wisely.
>
> --
> Jon Harder
> Technology Coordinator
> Mountain Lake Public School
> Mountain Lake, Minnesota
>
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