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Write Balance
On our VMAX, using FAST VP, noticed that a set of SATA disks was using roughly 50% less capacity than the other SATA disks. We started a Write Balance on the pool, but have only observed the disks with a higher capacity are increasing in used space and the disks with the 50% less are decreasing in used space, although very slowly. Is there any details on how the Write Balancing works? The process has been running for 6 days, and we were under the impression all the disks would get to an even point.
We have the rebalance variance set to the default of 1.
Quincy561
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September 19th, 2013 07:00
The rebalance is done on capacity. If you have mixed disk sizes in the same pool, they both will be balanced to the same percentage of capacity. So your larger disks will have more capacity used and more IOPs. This is why we do not recommend mixing drive sizes in any given VP pool.
atthomas1
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September 19th, 2013 09:00
We have the same size disks in the pool. We are coming up on a week, and the balancing is still running.
Quincy561
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September 19th, 2013 10:00
BTW, the rebalance variation sets when the rebalance should stop (close enough), it has nothing to do with how quickly it runs.
Quincy561
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September 19th, 2013 10:00
All the TDATs roughly the same size? The balancing is on a TDAT level, not at the disk level.
You said "observed the disks with a higher capacity are increasing in used space" so I thought some were different sizes.
atthomas1
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September 19th, 2013 11:00
Yes, tdats are pretty much the same size.