On Sat, 7 Jan 2012, Jim Klimov wrote:


Several RAID systems have implemented "spread" spare drives
in the sense that there is not an idling disk waiting to
receive a burst of resilver data filling it up, but the
capacity of the spare disk is spread among all drives in
the array. As a result, the healthy array gets one more
spindle and works a little faster, and rebuild times are
often decreased since more spindles can participate in
repairs at the same time.

I think that I would also be interested in a system which uses the so-called spare disks for more protective redundancy but then reduces that protective redundancy in order to use that disk to replace a failed disk or to automatically enlarge the pool.

For example, a pool could start out with four-way mirroring when there is little data in the pool. When the pool becomes more full, mirror devices are automatically removed (from existing vdevs), and used to add more vdevs. Eventually a limit would be hit so that no more mirrors are allowed to be removed.

Obviously this approach works with simple mirrors but not for raidz.

Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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