Re: Recovery from full metadata with all device space consumed?

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On Thu, Apr 19, 2018 at 04:12:39PM -0700, Drew Bloechl wrote:
> On Thu, Apr 19, 2018 at 10:43:57PM +0000, Hugo Mills wrote:
> >    Given that both data and metadata levels here require paired
> > chunks, try adding _two_ temporary devices so that it can allocate a
> > new block group.
> 
> Thank you very much, that seems to have done the trick:
> 
> # fallocate -l 4GiB /var/tmp/btrfs-temp-1
> # fallocate -l 4GiB /var/tmp/btrfs-temp-2
> # losetup -f /var/tmp/btrfs-temp-1
> # losetup -f /var/tmp/btrfs-temp-2
> # btrfs device add /dev/loop0 /broken
> Performing full device TRIM (4.00GiB) ...
> # btrfs device add /dev/loop1 /broken
> Performing full device TRIM (4.00GiB) ...
> # btrfs balance start -v -dusage=1 /broken
> Dumping filters: flags 0x1, state 0x0, force is off
>   DATA (flags 0x2): balancing, usage=1

   Excellent. Don't forget to "btrfs dev delete" the devices after
you're finished the balance. You could damage the FS (possibly
irreparably) if you destroy the devices without doing so.

> I'm guessing that'll take a while to complete, but meanwhile, in another
> terminal:
> 
> # btrfs fi show /broken
> Label: 'mon_data'  uuid: 85e52555-7d6d-4346-8b37-8278447eb590
> 	Total devices 6 FS bytes used 69.53GiB
> 	devid    1 size 931.51GiB used 731.02GiB path /dev/sda1
> 	devid    2 size 931.51GiB used 731.02GiB path /dev/sdb1
> 	devid    3 size 931.51GiB used 730.03GiB path /dev/sdc1
> 	devid    4 size 931.51GiB used 730.03GiB path /dev/sdd1
> 	devid    5 size 4.00GiB used 1.00GiB path /dev/loop0
> 	devid    6 size 4.00GiB used 1.00GiB path /dev/loop1
> 
> # btrfs fi df /broken
> Data, RAID0: total=2.77TiB, used=67.00GiB
> System, RAID1: total=8.00MiB, used=192.00KiB
> Metadata, RAID1: total=4.00GiB, used=2.49GiB
> GlobalReserve, single: total=512.00MiB, used=0.00B
> 
> Do I understand correctly that this could require up to 3 extra devices,
> if for instance you arrived in this situation with a RAID6 data profile?
> Or is the number even higher for profiles like RAID10?

   The minimum number of devices for each RAID level is:

single, DUP:     1
RAID-0, -1, -5:  2
RAID-6:          3
RAID-10:         4

   Hugo.

-- 
Hugo Mills             | Gentlemen! You can't fight here! This is the War
hugo@... carfax.org.uk | Room!
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                        Dr Strangelove

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