On Tue, Jun 18, 2019 at 02:50:34PM -0400, Austin S. Hemmelgarn wrote: > On 2019-06-18 14:45, Hugo Mills wrote: > >On Tue, Jun 18, 2019 at 08:26:32PM +0200, Stéphane Lesimple wrote: > >>I've been a btrfs user for quite a number of years now, but it seems > >>I need the wiseness of the btrfs gurus on this one! > >> > >>I have a 5-hdd btrfs raid1 setup with 4x3T+1x10T drives. > >>A few days ago, I replaced one of the 3T by a new 10T, running btrfs > >>replace and then resizing the FS to use all the available space of > >>the new device. > >> > >>The filesystem was 90% full before I expanded it so, as expected, > >>most of the space on the new device wasn't actually allocatable in > >>raid1, as very few available space was available on the 4 other > >>devs. > >> > >>Of course the solution is to run a balance, but as the filesystem is > >>now quite big, I'd like to avoid running a full rebalance. This > >>would be quite i/o intensive, would be running for several days, and > >>putting and unecessary stress on the drives. This also seems > >>excessive as in theory only some Tb would need to be moved: if I'm > >>correct, only one of two block groups of a sufficient amount of > >>chunks to be moved to the new device so that the sum of the amount > >>of available space on the 4 preexisting devices would at least equal > >>the available space on the new device, ~7Tb instead of moving ~22T. > >>I don't need to have a perfectly balanced FS, I just want all the > >>space to be allocatable. > >> > >>I tried using the -ddevid option but it only instructs btrfs to work > >>on the block groups allocated on said device, as it happens, it > >>tends to move data between the 4 preexisting devices and doesn't fix > >>my problem. A full balance with -dlimit=100 did no better. > > > > -dlimit=100 will only move 100 GiB of data (i.e. 200 GiB), so it'll > >be a pretty limited change. You'll need to use a larger number than > >that if you want it to have a significant visible effect. > Last I checked, that's not how the limit filter works. AFAIUI, it's > an upper limit on how full a chunk can be to be considered for the > balance operation. So, balancing with only `-dlimit=100` should > actually balance all data chunks (but only data chunks, because you > haven't asked for metadata balancing).
That's usage, not limit. limit is simply counting the number of block groups to move. Hugo. -- Hugo Mills | Great films about cricket: Umpire of the Rising Sun hugo@... carfax.org.uk | http://carfax.org.uk/ | PGP: E2AB1DE4 |
signature.asc
Description: Digital signature
