A quick and easy performance improvement
mailscanner at ecs.soton.ac.uk
Wed Jul 26 19:26:12 IST 2006
Richard Lynch wrote:
> Julian Field wrote:
>> Richard Lynch wrote:
>>> uxbod wrote:
>>>> Why not hold the bayes on a RAM partition, and have a cronjob that
>>>> periodically backs it up throughout the day so that changes are not
>>>> lost if the server crashes ?
>>> That would definitely improve things. Seek time in RAM is zero!
>>> While monitoring disk I/Os (iostat 1) I was surprised at the high
>>> number for bayes. I didn't expect to see it so high. One my systems
>>> it was actually higher than the I/O for the mail queues.
>> That's very interesting.
>> Most people these days just use 1 big partition for / and nothing
>> else. So it won't be available to them. So why is this an improvement
>> when /var/spool and /.spamassassin are on the same partition? I can
>> see why, if they are on different partitions, though you're still
>> relying on the mapping of sector number --> physical hard disk
>> location. But if / and /var/spool are on the same partition anyway,
>> why would it run any faster?
> I can't see why it would either. If you're using one large partition
> changing the directory structure wouldn't be worth anything as far as
> performance goes. In my case they are on different partitions.
>> I am sorely tempted to say that you have merely cancelled out the
>> speed slowdown caused by splitting / and /var onto different
>> partitions. If they are both on the same partition anyway, and are
>> being written to a lot, they will end up very close to each other by
>> virtue of how the filesystem is likely to work.
>> I think that splitting / and /var slowed your system down. You have
>> just cancelled that out.
> I think you're right. Is it uncommon to have / and /var on different
> partitions? The sysadmins here argue for separate partitions because
> it lessons the likely hood of the rootfs filling up. They say that it
> can hose your system to the point that you can't even logon to fix it.
> So, we split / and /var (and others). I think all of our unix systems
> are that way. Is this a bad practice?
I have found in the past that splitting the installation into many
different partitions just causes more problems than it solves. Putting
/var separate on Solaris is a classic example. People say "when your
logs get big it won't fill /" which is true enough. But disks are huge
and cheap these days. Why not just do it properly and roll your logs
properly so they never occupy a lot of space? If you have them separate,
then as you install more patches, /var/sadm will start to get very
large, which there is nothing you can do about, so after 2 or 3 years
your /var will fill and you'll have to start bodging things to get them
out of /var to give you more room for /var/sadm.
I just find it causes more problems than it solves, so long as you set
up your system to maintain itself properly. If you never roll
/var/log/maillog on a MailScanner system then yes, it will get very
large, but set it up properly and keep your logs and quarantines pruned.
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