Average Disk write time throttled periodically on exchange server

I've been observing this for quite awhile, and I'm not sure what I should make of it. I have an Exchange 2003 Server running Windows 2003. I've noticed that at least IMAP service gets slowed to a crawl periodically, and at the same time I see on the perfmon that my Avg Disk write time, Avg Disk Que length, Avg Disk bytes write, and Avg Disk Bytes transfer all max out. I'm assuming that would be an indication of poor disk speed. I have a 3ware RAID 5 controller 9550SX-4LP. The firmware is out of date. Could that be the problem? I don't see any errors reported in the controllers logs. What else should I look for? It's a tough problem to troubleshoot because anything I can think of to try means taking the server down, and it's our only email server. How would an expert handle this? I also seem to be the only person who notices, other than the other admin who also uses IMAP. Everyone else has an exchange account, and I don't think it's been affecting them. Any suggestions would be helpful.
numb3rs1xAsked:
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MesthaCommented:
Do you have only a single RAID array? If so then that will be a major bottleneck on any Exchange server.
Firmware out of date is unlikely to have much of an impact, but if you can update it I would.

Start with the Exchange Troubleshooting tool - which you can download from Microsoft via http://exbpa.com/ 

Simon.
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numb3rs1xAuthor Commented:
I ran that tool, and it's telling me that compression should not be enabled on the mailstore drive. I can turn it off, but I wonder if there is any risk I should consider before doing so?
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MesthaCommented:
Well the only risk is that you don't have enough space.
Compression is a significant performance hit and should never be enabled on a server - particularly with the cost of storage so cheap these days.

Simon.
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numb3rs1xAuthor Commented:
ok. I cleared the transaction logs with an ntbackup and there is plenty of available space on the drive. Do I have to stop the exchange services in order to disable compression or will it successfully disable transparent of the services that access it?
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MesthaCommented:
I wouldn't make the change with Exchange running.
Stop all the services and then make the change. Then wait for the files to be decompressed. You want to have as few things accessing the drive as you can, so if it also holds files make sure that no one is accessing them.

Simon.
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numb3rs1xAuthor Commented:
We are running Exchange 2003 standard with the registry setting that allows the 75GB maximum on the mail store. the mail store is about half full. If I decompress the filesystem containing the store, does that mean the store will also expand?
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MesthaCommented:
The file sizes listed in Explorer shouldn't change so the store itself shouldn't increase, as that isn't how disk compression works.

Simon.
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