Defrag

[Paul Egan]

Hi.

I'm running a HP Prolient ML530 G2 (RAID 1)
with 2 18.2 U320 15k disks.

Should I use the standard W2k defrag tool or is there something more powerful.

Also, should I defrag with both disks connected or just do one and when I put in the second to start the mirroring it auto defrags the second by copying accross the defraged version of the first disk?

[CA1028844 · Accepted solution]

Whether you use the Win2k defrag tool, or a third-party tool (such as the Disk Optimizer in Symantec's Norton System Works) is completely personal preference. Many people are successfully using the Windows defrag tool, as well as many others successfully using third-party tools. You might want to research these other defrag utilities, and see if you feel they are appropriate to your environment, budget, requirements, etc.

With regard to defrag and mirroring, for all practical purposes, it does not matter when you insert the drive.

(Note: For the purposes of this discussion, I'm going to assume you setup your mirrored array properly. By that, I mean that you setup your RAID array first, then pulled out one of the disks, then proceeded to install your OS and software, etc. If you setup your array as a single drive RAID 0 array, then you will have to either migrate the array or destroy it and create a mirrored RAID array in its place.)

Theoretically, if you defrag the volume first, and then insert the mirror drive, you would be saving some "low-performance" time. This is so because the re-mirroring would only have to copy each block over once, and the blocks would already be in defragmented order. And while this copy is being performed, there is some degradation in read performance to the array. So the only real reason to do this is if you absolutely have to minimize this "low-performance" window.

However, for all practical purposes, there is no real difference. If you mirror the drives first, and then defragment, as each block is moved on one drive, the corresponding block is also moved on the mirrored drive at the same time. Although this theoretically increases the amount of time that mirrored writes are occurring (i.e. first the drives have to completely mirror, then as you defragment more writes are having to be mirrored), this is really no different than doing normal writes on this array anyway.

In other words, your OS will be writing out to its page file, and other write activity will be occurring on this array during normal daily operations. The defrag is merely a "heavy I/O" period for the OS array -- with the attendant performance penalties for this.

So in short, there is no real difference between these two methods. You can insert the drive immediately, or you can wait until after the defrag. I would argue that if a window of heavy I/Os on this array is going to cause so many problems that you absolutely have to minimize it at all costs, then you are already in trouble and need to re-think and re-size your solution.

[Paul Egan]

Ahh, that for the detailed reply. answered pretty much all my questions. My problem was that the system is in production 24/7 and had no way to take it out of the network to defrag in peace so thought I could do one disk at a time in a backup server.

Thanks again :)