Defragging Raid drives.
 

When you're defragging a Raid one setup, that's twin drives with identical files on the second drive, does Win XP defrag the second drive simultaenously?
Cheers.

Hi Allan..........
 

Think that goes top of my "Q of the week".

Really made me think, that one.

I honestly don't know the answer, but a bit of grey cell bashing makes me surmise the negative. As the drives in a Raid config do not need to be identical in any way (and even if they were, there's no reason to believe the files would be identically placed on each drive) then I figure each drive is treated individually.

The defrag software would not be aware of the copy on the other drive nor does it need to (the Raid software is doing that) so, logic dictates the defrag will do what it usually does if fed to a string of drives - start at the top and work down. Quite how it selects which of the drives to start on first is a mystery.

Not sure if that's been any help at all.


CS

The way I understand a raid one, windows sees them as one drive, the information is treated identically. of course, its possible my thinking is wrong...

I think Chris really hit on the key point here, in that it's not Windows that determines what the second drive does, but the RAID management software. It may simply send duplicate read/write commands to the second drive no matter what it's fed.

My guess is that both drives are defragged, as the management configuration probably can't tell the difference between a defragmentation and typical read/write access.

Guys, some ferreting around reveals, defragging a Raid 1 set-up does do both drives simultaneously.

But try 'error checking' ...using Win XP Pro, it took over 2 hours to error check 74 (alias 148) Gigs on a Raid 1 2TB My Book external drive.

What's it gonna be like if ever I manage to fill the thing up, like to set it off just before I go on holidays.

Not sure ..
 

Hi Chaps,

RAID0 (I use) treats two discs as one and therefore defrags as one. It would make sense to me that RAID1 was defragged disc by disc starting with the disc of your choice if doing it manually or however you have scheduled defrag to run - 1 only or 1 and others.

I would think it would be out of scope for it to be able to defrag two independent discs at the same time as there would be way too much processing to complete when trying to establish contiguous files.

Simple answer to this is try it - if it won't - it won't, there should be no harm done in any event.

Cheers
Dave

Hi Dave, the RAID1 system mirrors the data to 2 drives simultaneously; from my research so far, so does defragging a RAID1 rig.

Cheers.

even common sense says each bit on each drive must be in identical places, using the same address. thats why its a "mirror". if one drive was fragmented, and the other was not, the information would have to be read at separate times for each drive, and written separately.

Exactly Allen; I've got 2 years of clips, for an aircraft restoration society on a 2TB WD My Book RAID1 rig. 280GB so far, I defrag after every session.

Backing that up is another story however.

Cheers.