Defragging and raid 0

How does defragging work on two harddrives in a raid 0 setup? I'm using diskkeeper and it won't work on my PC(raid), yet it's working on my laptop. Is this because of the raid setup?

Ok background info, how DOES defragging work on a raid setup? each harddrive is defragmented seperately?

Good question. I've just been using the stock 2k defrag utility on my RAID 0 setup...

It would work the same as it would on a single drive pretty much. Since the adjacent blocks are written (AFAIK) in corresponding spots on each hard drive. I.e. You've got two blocks of information. Block one is written on sector 15 of the first hard drive and block two is written on sector 15 of the second one.

It has to do with the way the drive is mapped. The o/s sees it all as one big drive. It can't tell if you've got one big drive or 4 small ones combined into a big one via raid. The defrag program says to write the block of information to a certain part of the hard drive. The RAID controller gets that sector and redirects it to the appropriate spot on the appropriate drive.

I could of course, be way off base here. But I THINK that's how they work. Haven't really looked into it much though.

Ultimately it wouldn't really matter. The file should be contigous on both drives so that the blocks of each are together.

It basically works like that, although the stripe size is usually more than 1 block (because it's faster to read a whole bunch of blocks at once from one disk than to swap back and forth constantly for one small read). So you'd have (for example, with a stripe size of 16 blocks) blocks 1-16 in sectors 1-16 of disk 1, then blocks 17-32 in sectors 1-16 of disk 2, then blocks 33-48 in sectors 17-32 of disk 1, etc...

It *shouldn't* matter to the program doing the defragging what the underlying disk structure is (it could be a virtual RAM disk for all it knows), but that particular program (haven't used it) may be trying to do low-level things to the disk that just don't work with your RAID controller. AFAIK, the built-in Windows defrag and the one with Norton Utilities both work with RAID setups without a hitch, so I'd use one of those.

Thanks guys

Well I know disk keeper allows you to do stuff like defrag your Pagefile (which requires a re-boot and may happen before drivers, like ones for your RAID are loaded) and stuff so I would not be surprised if, as matthias99 said, it was trying to do low lvl stuff that it can't do.

Well in the case of the page file, I think it's more because Windows won't let other programs access it. It should still be transparent to it. Think of it this way. If you've got RAID and boot to DOS, you can still see the drive as a normal single hard drive. It should be transparent in the same way.

Avatar28 said:

Well in the case of the page file, I think it's more because Windows won't let other programs access it. It should still be transparent to it. Think of it this way. If you've got RAID and boot to DOS, you can still see the drive as a normal single hard drive. It should be transparent in the same way.

Click to expand...

But does windows xp/2k run on dos?

Besides, no matter the OS, if you don't have the drivers installed it won't show up as one drive, or maybe not even show up at all if it can't load the card (assuming you have a RAID card rather than oboard (native) PATA RAID or onboard native SATA raid). Besides I was only supporting his hypothosis as to why this program wouldn't work. You may be right but its the only answer that makes any sense at all :/