Exchange Defrag 1

[hesaloser]

All,
After doing a windows disk defrag analysis on an exchange partition I found:
Volume size: 45 Gb
Percent free space: 54%
Total frag: 49%
File frag: 98%
Pagefile has no frags
MFT has 2 frags
The two most fragmented files are the MDBDATA\ 15.6 Gb .edb and 4.5 Gb .stm with 2,000 frags and 645 respectively.

Question being, what steps are necessary to prepare exchange for proper online or offline defrags, and what would you recommend be my first step in trying to repair the state of this partition?

I’ve read both positive and negative things about offline defrag using eseutil, and also have heard that running windows defrag on an exchange database can be harmful because of its intensive I/O process.

 

[58sniper]

Nothing for online defrags, as the server does that automatically. You can verify that by checking the 1221 events in your event log.

Do NOT - under ANY circumstances, run a Windows or 3rd party defrag progam on an Exchange volume while databases are mounted.

Based on your results, you have the paging file on the same volume as Exchange? The databases should be on a dedicated array, and so should the log files.

As for eseutil, that would depend on the amount specified in the 1221 events. Unless it's a massive amount (many GB), I would refrain from doing an offline defrag.

Pat Richard
Microsoft Exchange MVP

 

[hesaloser]

Pat,
The paging file is on a separate partition as the exchange data, as for disks, we have (3) 72.8 Gb drives in a RAID-5 array. We don’t really have the means to put the database files on a separate dedicated array, as much as I wish we could, we can’t. As of this morning event id 1221 reported 5 Mb of free space. I have never unmounted an exch database, are there any special instructions or precautions to follow before unmounting? Is it as simple as going into system manager, selecting first storage group, mailbox store, dismount store, selecting public folder, dismount store?

 

[xmsre]

This is a bad design.

1. The RAID 5 write penalty is too high. You should be using RAID 1 or 10.

2. The database files are on the same disk as something else; presumably the logs, and competing with other logical disks on the same physical spindles for a very limited IOPS capacity.

If you have few enough users that a 3 disk RAID 5 will support your IO load, then RAID 1 is a better choice. With two spindles you get the same read throughput and twice the write throughput using RAID 1 over a 3 disk RAID 5 set. The file level fragmentation is moot for the database files: the disk is accessed randomly. If you put the logs there, this could have a negative impact on log performance depending on how fragmented your logs are. When in a limited spindle count situation, you can use logical drives to segregate the files and prevent file level fragmentation. This does not help you in terms of IOPS capacity, and does not address comingling. For Exchange, you should really consider

1. a mirror for the OS & pagefile
2. a mirrror for the logs
3. a mirror or RAID 10 for the database sized for your IOPS load.

I would not do a file level defragmentation; you wouldn't be solving anything because the underlying disk layout is not changing.

I would not do an offline exchange defragmentation; your 1221 shows that there is nothing to gain and you would actually hurt performance (

http://msexchangeteam.com/archive/2004/07/08/177574.aspx)

An online exchange defrag is already done automagically

I would measure the IOPS load, buy an appropriate number of spindles, and configure the disk accordingly.

John

 

[58sniper]

And a star for John, who is always much better at explaining disk performance than I.

Pat Richard
Microsoft Exchange MVP

 

[hesaloser]

So in the meantime, since it will take awhile before the talks of redesigning can occur... Am i SOL? or what else can I do in the meantime to help with the fragmentation?

Thanks for you responses,
Much appreciated!

 

[58sniper]

I'd leave that alone. Those files are always fragmented, and get so just during normal use, since that's where all of your user email is stored.

Pat Richard
Microsoft Exchange MVP

 

[Excalibur1701]

If you have the drive space, you can do a eseutil on your information store. When this occurs, it creates a brand new file, which, I assume won't be as fragmented when it writes it.