Re: [webmin-l] High I/O usage issues which may be related to Usermin...

[Jamie C. <jca...@we...>]

On 6/Oct/2006 12:06 Jesse C. Smillie wrote ..
> Hello once again everyone.  Since the new school year started we have 
> been noticing increasingly high I/O usage on our servers.  When I run 
> the top command quite often you will see the WA status swing from really
> low up into the 70-80 even 90% range for up to a min and then drop 
> again.  I spend a little time trying to track down the problem and have
> noticed the following:
> 
> When I/O is really high I always see the following line in "ps aux | 
> grep D":
> 1229     14619  0.8  0.2  37272 16520 ?        D    14:43   0:00 
> /usr/local/usermin-1.230/mailbox/delete_mail.cgi
> 
> (Note: User ID is normally not the same one when polled)
> 
> Sometimes I also see the index.cgi file too, but no where near as much
> as the above.
> 
> A coworker in our department had made mention that maybe whats happening
> has something do with the process that usermin uses to remove mail from
> a mailbox when its deleted.  Something about compacting the box during
> the delete instead of doing it like Thunderbird and waiting to compact
> until space can be saved.   I guess case being all the reading and 
> rewriting required to removed the dead message from the box.
> 
> I don't recall having this problem that bad last year.  On occassion 
> when almost everyone was logged in things would get a little screwy, but
> not like this.
> 
> General information about our config:
> Server:
> Processors: Dual Opteron 242's
> Ram: 6Gig ECC DDR
> HDs: 1.2 TB 3ware Raid Array
> OS: Slamd 64 10.2b (Slackware more or less)
> Kernel: 2.6.18
> Usermin Version: 1.230 (This was happening in the last version too 
> however.  I just upgraded two days ago to see if the problem went away)
> 
> Unfortunately dealing with I/O problems isn't my speciality so I could
> be barking up the wrong tree here.  Any suggestions would be greatly 
> appriciated as always...

What format are your mailboxes in? If they are in mbox format (one file per
user), when Usermin deletes email it will re-write out the entire mail
file with the removed emails taken out. As you might expect, this could cause
substantial disk IO on large mail files..

The solution I used was to switch to Maildir format, in which each email is stored
in a separate file. Deleting from this format is much quicker..

 - Jamie