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June 2nd, 2010 09:00
disk wrapping vs overallocation
I have a V-max with 64 FC drives and around 32 SATA drives.Planning to use RAD5(7+1) on FC and RAID6(14+2) for SATA drives.
At present planning to stick standard LUN sizes with 34GB across V-max like traditional DMX.Challenge is how to prevent disk wrapping at the same time conserving the space on the metas.
I will be more specific.With 34GB LUN size,max of 8-way meta be created (272GB size)..if the required volume size is 300GB,then it creates a disk wrapping on one of the RAID group or 2 times of 272GB to aviod wrapping which lots of space being wasted.Same thing applies for SATA.
How to balance between disk wrapping vs overallocation?
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RRR
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June 3rd, 2010 05:00
With only 64 drives and unsing 7RAID5, you can have 8 members per meta indeed (64/(7+1)). Why would you stick to 34GB per symdev ? Wrapping should be avoided in striped metas, since having a disk (or more) in the same meta will cause unwanted drive's head movements. Try to keep the physical latency as low as possible when you can, so keep a single full stripe on separate disks and don't wrap. I'd increase the symdev size. There's no real need to hang on to 34GB, which is just a nice number.