Defragging a RAID 5

Posted on 2004-10-05
Last Modified: 2009-02-14
Simple question... perhaps a more complicated answer:

Is defragging a RAID 5 array good, bad or a useless waste of time???

My guess would be that it's a waste of time because of the data scattering nature of RAID 5.

Question by:Jared Luker
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LVL 57

Expert Comment

by:Pete Long
ID: 12231901
No Jared - your guess is off the mark :(

The striping is done at a hardware level the OS has nothing to do with it, de-fragging deals with the storage of "non-contigious" files that are split up because of the way files are stored at a cluster level that is handled by the file system of the drive NOT the type of volume/partition
LVL 17

Author Comment

by:Jared Luker
ID: 12232018
I didn't say the OS had anything to do with it.  

I stated that with raid 5, or raid 0 for that matter, the data gets scattered all over however many drives you have.  I don't see what good a defrag would do.  It seems to me that a defrag of a RAID 5 stripe set would just move pieces of files or pieces of directories around the raid array.  Is there even such a thing as "contiguous" with RAID?
LVL 57

Accepted Solution

Pete Long earned 350 total points
ID: 12232121
>> Is there even such a thing as "contiguous" with RAID?

Yes, regardless of the "Parity striping of Raid" is designed for speed and resiliance, where as bit mirroring is only concerned with resiliance.

regardless of how things are stored at a hardware level the info is placed on the drive on an in-efficiant cluster sorage system - the only thing that sees the segragated bit level of RAID is the RAID controller (unless we are talking software RAID)

every hard drive no matter what its formatted as is a big grid of pigeon holes that are mapped (at a digital/OS level) de-fragging sorts that out

>>I didn't say the OS had anything to do with it.

no but even defragging from command line needs at least a 16 bit  operating system enviroment to run
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Assisted Solution

by:Duncan Meyers
Duncan Meyers earned 150 total points
ID: 12232277
To add to PeteLong's remarks, I've seen backup times halved by defragging a badly fragmented RAID 5 array. It's worth doing...
LVL 17

Author Comment

by:Jared Luker
ID: 12239217
Should I get something special to defrag it with, or does the windows defragger or even disk keeper light work OK?

LVL 57

Expert Comment

by:Pete Long
ID: 12251106
Nope - disk manager and defrag is all you need :)
LVL 57

Expert Comment

by:Pete Long
ID: 12251938

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