Christian Pernegger wrote:
Hi list! Sometimes I want to exchange a drive in an array even if it hasn't actually failed, e. g. - in preperation for a grow operation: exchange-resync-exchange-resync-...-grow - when removing old drives as part of regular maintenance - ... Currently one has to fail an active drive to trigger a resync to the replacement (assuming it was added as a spare beforehand) and thus suffer the loss of fault tolerance and performance until the sync is complete. Suggestion: allow adding drives as an explicit replacement for an active one. The active drive would then be copied to the new one in the background, effectively replacing the component device with a mirror. Bonus points if the resulting setup is a valid mode of operation and not just a temporary hack. I suppose one could see the feature as a special case of the reshaping that's all the rage now :)
I think what you want is a subset of the problem many of us face, moving a member of an array to a larger partition on a (much) larger drive. That migration, followed by a grow, is getting more appealing, as various drive drop to "prize in a cereal box" pricing. And as data grows, backup to something other than disk is getting pretty impractical, resulting in unit upgrades to save space, time, power, etc, etc.
I agree with the need, I have several ugly methods of doing this which boil down to replacing a member with a raid-1 of the member and the new drive. I have done it several ways, including the "I can't fit another drive in the box" solution, using nbd and write mostly. Uglier than a hedgehog's ass, but it worked... eventually.
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