Defragging Raid drives. at DVinfo.net

Allan Black · January 17th, 2008, 05:05 PM

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.

Chris Soucy · January 17th, 2008, 05:20 PM

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

Allen Plowman · January 17th, 2008, 05:35 PM

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...

Ben Winter · January 17th, 2008, 06:28 PM

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.

Allan Black · January 18th, 2008, 04:34 PM

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.

Dave Gosley · February 8th, 2008, 11:42 AM

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

Allan Black · February 8th, 2008, 05:00 PM

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

Cheers.

Allen Plowman · February 8th, 2008, 05:06 PM

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.

Allan Black · February 8th, 2008, 05:18 PM

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.

January 17th, 2008, 05:05 PM	#1
Allan Black Inner Circle Join Date: Sep 2006 Location: Sydney. Posts: 2,928	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.

January 17th, 2008, 05:20 PM	#2
Chris Soucy Inner Circle Join Date: Feb 2007 Location: Fairfield, Dunedin, New Zealand Posts: 3,691 Images: 18	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

January 17th, 2008, 06:28 PM	#4
Ben Winter Trustee Join Date: Jun 2005 Location: Hollywood, CA Posts: 1,675 Images: 1	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. __________________ BenWinter.com

February 8th, 2008, 11:42 AM	#6
Dave Gosley Major Player Join Date: Oct 2007 Location: Hampshire Posts: 226	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 __________________ http://www.videoproductionshampshire.co.uk

February 8th, 2008, 05:06 PM	#8
Allen Plowman Major Player Join Date: Oct 2007 Location: Paradise, california Posts: 353	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. __________________ "What I need is an exact list of specific unknown problems we might encounter."

January 17th, 2008, 05:35 PM	#3
Allen Plowman Major Player Join Date: Oct 2007 Location: Paradise, california Posts: 353	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...

January 18th, 2008, 04:34 PM	#5
Allan Black Inner Circle Join Date: Sep 2006 Location: Sydney. Posts: 2,928	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.

February 8th, 2008, 05:00 PM	#7
Allan Black Inner Circle Join Date: Sep 2006 Location: Sydney. Posts: 2,928	Hi Dave, the RAID1 system mirrors the data to 2 drives simultaneously; from my research so far, so does defragging a RAID1 rig. Cheers.

February 8th, 2008, 05:18 PM	#9
Allan Black Inner Circle Join Date: Sep 2006 Location: Sydney. Posts: 2,928	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.