From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Feature request: ability to exchange drive without failing the old one Date: Tue, 13 Oct 2009 16:38:12 -0400 Message-ID: <4AD4E534.2010102@tmr.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Christian Pernegger Cc: Linux RAID List-Id: linux-raid.ids 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. -- Bill Davidsen Unintended results are the well-earned reward for incompetence.