A quick and easy performance improvement

[Scott Silva]

DAve spake the following on 7/26/2006 12:22 PM:
> Julian Field wrote:
>>
>>
>> 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.
>>
> 
> I got on board after I sent the message, sorry about that.
> 
>>>
>>> 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)
> 
> I had a tape once, the drive failed and after three months we never did
> get another drive to read the old tapes without errors. Never trusted
> tapes much after that. Certainly after HP said "Sometimes that happens,
> it's a head alignment issue. Have you tried another old drive?". Now I
> backup to a RAID, to each his own.
> 
> I love trolls, and lists that cover mail products attract so many!
> Though, oddly enough, this list doesn't... hmmmm... I have to subscribe
> to qmail/sendmail/postfix/procmail lists to witness really *good*
> flames. What am I to make of that?
> 
> DAve
> 
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