A quick and easy performance improvement

Julian Field mailscanner at ecs.soton.ac.uk
Wed Jul 26 19:42:11 IST 2006

DAve wrote:
> 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.
>>> Thoughts?
> Maybe I am showing my ignorance but how? I'm not seeing any performance 
> issues myself, just curious. I currently have bayes on one 
> controller/disk pair and the queues on another controller/disk pair. 
> I've always believed that to be about the best you could do.

On a different controller/disk pair you will get better performance as 
you can read/write in parallel. But we were talking about putting the 
whole setup on one disk where you have to read/write one at a time.

> Of course it just takes 2 minutes in a terminal if I should move bayes 
> to the same controller/disk as the queues.
>> 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?
>> -- Rich
> I have always used separate partitions, though others who do as well 
> have told me I am stupid because I use different partitions than they 
> do, everyone has an opinion ;^)
> I keep separate partitions for the sake of fsck, performance be damned. 
> I've lost data on the far side of a 70gb disk because I had a failure 
> fsck couldn't fix, (SATA drives and a sad story). I've isolated /, /tmp, 
> /var, /usr, /data ever since. I keep websites, backups, ftp directories, 
> mail queues, etc in /data. Depending on the task the server is doing.

That's fair enough, that's your choice. Bad experiences with fsck will 
change your way of working. Personally, I haven't had that trouble, and 
I always have a reliable well-tested tape backup system in place to 
handle that, so it's never bitten me badly. But you are quite entitled 
to your own opinions based on your own experiences, I don't think anyone 
could have a problem with that, except the trolls :o)

> DAve

Julian Field
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