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Old 02-24-06, 09:03 PM   #7
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Join Date: Feb 2006
Posts: 1
Default Re: mdraid vs. dmraid benchmark and Intel RAID0/RAID1 on same pair of drives


On your last post you mention doing a combination of paritions across disks to obtain stripping and mirroring of different filesystems. This is not a good idea performance wise. Any access to the mirrored partition pair would cause a slow down in performance of the striped parititions (and vice-versa) as they contend for the same set of heads on the discs. A drive can only execute one seek at a time so if a drive is being queried by the stripe and the mirror simultaneously the drive will have to jump around a lot. This is also true for multiple partitions on the same drive pair if you were only mirroring but it is my belief that it would be more efficient since it has only one RAID type to deal with. Most Mirroing implementations do round-robin reads to boost read performance and write simultaneously to both drives without penalty. Striping (raid 0/5) reads chunks based on the stripe size across all of the drives in the set. The same goes for writes. I would guess to say that the penalty for mixing them on the same set of drives would be substantial if both sets of virtual RAIDs were busy simply due to the different nature of how each type of RAID treats the drives.

Just an opinion (not entirely backed up by scientific fact)
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