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Fragmenting RAID volumes

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Does defragmenting a Raid volume... Say Raid1 or Raid5 make any sense?

How about software vs. hardware raid on this topic?

How does it work? Someone with the knowledge care to explain? :)

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Does defragmenting a Raid volume... Say Raid1 or Raid5 make any sense?

How about software vs. hardware raid on this topic?

How does it work? Someone with the knowledge care to explain? :)

The same reasoning to defragment a non-RAID volume on a single hard drive applies to a volume on a RAID array. If the files aren't fragmented, then the RAID controller and/or OS can do a better job of caching data so that the array seems to perform better.

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Does defragmenting a Raid volume... Say Raid1 or Raid5 make any sense?

How about software vs. hardware raid on this topic?

How does it work? Someone with the knowledge care to explain? :)

The same reasoning to defragment a non-RAID volume on a single hard drive applies to a volume on a RAID array. If the files aren't fragmented, then the RAID controller and/or OS can do a better job of caching data so that the array seems to perform better.

I understand the reaosn... but... on a Raid5 for example... the files are already fragmented (the controller spans the files across the disks)... but the OS doesn't know that becuase it sees the disk as a whole.

So how does fragmenting a logical disk on a Raid5 work?

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Like you said the data on a RAID 5 array is on several disks but this does not mean it is fragmented. You should not see an array as 2 or more disks but as a single disk. RAID is actually only a means of improving performance and reliability for relatively little cost compared to what a disk would cost with equal performance and reliability. Just look at an array like your standard physical disk. When parts of a file are written all over the file system, the file is fragmented. When this is not the case, the file is not fragmented. Why? Because the way an array works. It starts reading at cluster 1 on disk 1, then cluster 1 at disk 2, cluster 1 at disk 3, then cluster 2 at disk 1, cluster 2 at disk 2 and so on. as the file system doesn't know about this, it just reads cluster 1, then cluster 2, then 3 and so on. For all practical purposes the array is a single disk and that's how the file system sees and uses it.

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I understand the reaosn... but... on a Raid5 for example... the files are already fragmented (the controller spans the files across the disks)... but the OS doesn't know that becuase it sees the disk as a whole.

So how does fragmenting a logical disk on a Raid5 work?

Fragmenting in logical disk is the same in RAID or multi disk volume. You want to maximize the continuous data in any single volume. This reduce software overhead, as well as seek within the same disk in the array. Unless you get the file to fragment exactly where the strip between disk split (almost impossible), a fragmented file will still be slower than a continuous one.

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