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Dell Poweredge 2800 PERC 4e Cache Running Exchange 2003

I am running exchange server
2 physical disks in RAID1 configuration
2Gig Ram

A bit of background......
The server has been running fine for years (1 Storage Group, 1 mailbox store), however I have recently gone through the process of adding another RAID1 to increase space, I created 2nd and then 3rd storage groups on the new array.  (I did Clear the config in the Perc Raid software (CTRL+M at boot and set it up again as it was)
This caused a severe degredation in performance.
I tried the 3G switch in the boot.ini file

Since then I have managed to reduce the mailboxes and have done a lot of moving mailboxes from one Storage Group to another, and from mailbox store to mailbox store.

I now have the original 2 physical disks in the server (RAID1) and have removed all the others I have split the data into 2 mailbox stores.but the perforamance is still very bad. I then tried splitting it accros storage groups....but still the same performance issue.
Working through the TroubleShooting Assistant for Exchange, It is highlighting bad disk performance....and using the performance monitor for Windows  the Ave.Disk Sec/Read and Write graphs are spiking all over the place....sometimes the graph shows both these running constantly at 100....however occasionally the graphs go all quiet and performance is ok.

I have now removed the 3G switch in the boot.ini file.

The demand on the server shouldnt have changed considerably, the user count is similar to always, and I am runng nothing else on the server.

I wondered if by Clearing the RAID config and resetting it up i have disabled the cache, it is set to DirectIO at the moment in the RAID setup. Does this mean the Cache is on or off?

I dont know what else to do...it is difficult for me to reboot the server as it is used almost 24/7

Thanks for any help in advance.
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1 Solution
Firstly when did you last defrag this filesystem?  Windows default is useless, use something like Raxio perfect disk or Disktrix Ultimate Defrag.

When you cleared the config, did you clear the cache settings?  Write-Back is the thing to pick, if it's something else (like write-through) that wouldn't be helping.  The penalty is that you'll almost certainly get a corrupted filesystem if the server looses power (with write-back) as there is every chance data have not yet made it to disk and are sat in the cache on the card.

The perc4e supports on-line capacity expansion and on-line raid level migration, so far as I can remember you can do raid1 to raid5 on-line on that card.  There is risk, the card can do it, but there are pitfalls and mistakes that could easily spoil your day :)

If you are confident you have a backup scheme that works (ie you tested it recently) or if you have a spare disk (in addition to the minimum 1 extra disk you'll need for the raid5) then you could pull a disk, mirror onto the spare and keep that handy in case of meltdown..  (yep, I am paranoid)

Ok, so the process is fairly simple.  Add a disk of at least the same size or larger, preferably another of the same ones already in there.   Once you do that, go into the array management utility, initialise the disk as a raid disk, add it as a member disk and pick raid5.

This will take a long time, I don't know how big the disks are, and performance will suck whilst its doing it.  If you loose power it might be all over, depends.  But then you have a backup ;)

Shout if you want more help on this!
"I wondered if by Clearing the RAID config and resetting it up i have disabled the cache, it is set to DirectIO at the moment in the RAID setup. Does this mean the Cache is on or off?"

Oops, off.  See above, still valid suggestions, but setting this to write-back will make a massive difference.  It's worth going into device manager, right click on the volume in the disks section, click properties and then policies I think it is, check that you've got cache etc enabled there too
dacoopeAuthor Commented:
Hi Thanks for you comments:

The following settings are on the logical drive in the Raid PERC software

Write Policy: WRBACK
Read Policy: ADAPTIVE
Cache Policy: DirectIO

Is this incorrect for optimal performance?
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No, that looks correct.
dacoopeAuthor Commented:
From what you have said, It sounds like the Write Policy is Correct

As for Read Policy, I could choose READAHEAD or NO_READAHEAD instead of adaptive
As for Cache Policy, I could choose CachedIO instead of DirectIO

What do you think?
dacoopeAuthor Commented:
Thanks for your help
At the moment I dont really want to mess around with the RAID side of things unless I absolutely have to

Defrag hasnt been run for some time...and only using the windows defrag.  Are the two you mentioned available for free download?
dacoopeAuthor Commented:
Thanks again
Unfortunately the performance is still bad, I shall try a defrag overnight (with windows software if I cant find any other)
Sadly not, they are not overly expensive though ~$50-70

If you do come to want to do the raid migration give me a shout, I'll talk you through it
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