I'm struggling with a btrfs RAID0 filesystem.

It's expanded on 4 disks but i need to remove one of those disks.

This is the current status of the filesystem:

[root@osgiliath detlev]# btrfs fi show /mnt/Data/
Label: 'Data'  uuid: 4c15fe81-ca58-4ac5-adf7-bdde245496f0
        Total devices 4 FS bytes used 1.26TiB
        devid    1 size 2.68TiB used 612.55GiB path /dev/sdc2
        devid    2 size 74.53GiB used 74.52GiB path /dev/sda1
        devid    3 size 931.51GiB used 606.55GiB path /dev/sdc1
        devid    4 size 232.89GiB used 7.52GiB path /dev/sdb

and df:

[root@osgiliath detlev]# btrfs fi df /mnt/Data/
Data, RAID0: total=1.26TiB, used=1.26TiB
System, RAID1: total=32.00MiB, used=112.00KiB
Metadata, RAID1: total=3.00GiB, used=1.66GiB
GlobalReserve, single: total=512.00MiB, used=143.50MiB

I tried deleting /dev/sdc1 but it failed with No space left on device. I tried rebalancing (only metadata first then data also). It balanced some data but now, if I try to delete /dev/sdc1, it moves some (4G) data out of sdc1 to sdb then stops with "No space left on device". If I rebalance, it moves data back from sdb to sdc1.

I tried removing sdb too but it just says No space left on device.

I am not sure how I can remove that /dev/sdc1 (I know, there are 2 partitions on the same disk, this is due to a broken disk connector, i had to move it temporarily, this is why I want it removed)

Any idea ?

  • 1
    Which kernel version? Especially if you're on something a fair bit older, can you try it with the latest kernel? btrfs changes fairly fast. – derobert Jan 9 '16 at 11:22
  • It's a kernel 4.1.15 Is it too old ? – Detlev Casanova Jan 9 '16 at 21:06

You could try resizing devid 4 (sdb) to be 0 bytes: btrfs filesystem resize 4:0 /mnt/Data/.

If that fails it might be because there is a subvolume on /dev/sdb, you can check with: btrfs subvolume list /mnt/Data/

If there is a subvolume I suspect you will have to delete it, after moving important data out of it, before you can remove the device. It might take a btrfs filesystem sync /mnt/Data/ before the subvolume is completely removed.

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