A quick and easy performance improvement

[Steve Campbell]

----- Original Message ----- 
From: "Scott Silva" <ssilva at sgvwater.com>
To: <mailscanner at lists.mailscanner.info>
Sent: Wednesday, July 26, 2006 3:57 PM
Subject: Re: A quick and easy performance improvement


> 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
>>
> If you want to see heated discussion, look back to the posts about 
> MailScanner
> and swap! ;-)

Did we ever finish that thread?

Steve
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