On Mon, Jun 25, 2012 at 10:46:01AM -0700, H. Peter Anvin wrote: > On 06/25/2012 08:21 AM, Chris Mason wrote: > > Yes and no. If you have 2 drives and you add one more, we can make it > > do all new chunks over 3 drives. But, turning the existing double > > mirror chunks into a triple mirror requires a balance. > > > > -chris > > So trigger one. This is the exact analogue to the resync pass that is > required in classic RAID after adding new media.
You'd have to cancel and restart if a second new disk was added while the first balance was ongoing. Fortunately, this isn't a problem these days. Also, it occurs to me that I should just check -- are you aware that the btrfs implementation of RAID-1 makes no guarantees about the location of any given piece of data? i.e. if I have a piece of data stored at block X on disk 1, it's not guaranteed to be stored at block X on disks 2, 3, 4, ... I'm not sure if this is important to you, but it's a significant difference between the btrfs implementation of RAID-1 and the MD implementation. Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- Never underestimate the bandwidth of a Volvo filled --- with backup tapes.
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