On Fri, Feb 01, 2002 at 04:55:18AM -0500, Arjan van de Ven wrote: > There is one thing that might spoil the device-mapper "just simple stuff > only" thing: moving active volumes around. Doing that in userspace reliably > is impossible and basically needs to be done in kernelspace (it's an > operation comparable with raid1 resync, a not even that hard in kernel > space). However, that sort of automatically requires kernelspace to know > about volumes, and from there it's a small step.... I think you're talking about pvmove and friends, in which case I hope the description below helps. - Joe Let's say we have an LV, made up of three segments of different PV's, I've also added in the device major:minor as this will be useful later: +-----------------------------+ | PV1 | PV2 | PV3 | 254:3 +----------+---------+--------+ Now our hero decides to PV move PV2 to PV4: 1. Suspend our LV (254:3), this starts queueing all io, and flushes all pending io. Once the suspend has completed we are free to change the mapping table. 2. Set up *another* (254:4) device with the mapping table of our LV. 3. Load a new mapping table into (254:3) that has identity targets for parts that aren't moving, and a mirror target for parts that are. 4. Unsuspend (254:3) So now we have: destination of copy +--------------------->--------------+ | | +-----------------------------+ + -----------+ | Identity | mirror | Ident. | 254:3 | PV4 | +----------+---------+--------+ +------------+ | | | \/ \/ \/ +-----------------------------+ | PV1 | PV2 | PV3 | 254:4 +----------+---------+--------+ Any writes to segment2 of the LV get intercepted by the mirror target who checks that that chunk has been copied to the new destination, if it hasn't it queues the initial copy and defers the current io until it has finished. Then the current io is written to *both* PV2 and the PV4. 5. When the copying has completed 254:3 is suspended/pending flushed. 6. 254:4 is taken down 7. metadata is updated on disk 8. 254:3 has new mapping table loaded: +-----------------------------+ | PV1 | PV4 | PV3 | 254:3 +----------+---------+--------+ _______________________________________________ linux-lvm mailing list linux-lvm@sistina.com http://lists.sistina.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html