A quick and easy performance improvement

[DAve]

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.

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.

DAve





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