Error while deleting device from a raid1 array

[Jiachen Yang <farseerfc@gmail.com>]

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Hi,

I'm sorry if this email is sent twice. Gmail says it failed to deliver
because it contains HTML, so I will try with plain text:

I have a raid1 array that contains 3 devices like this:

Label: 'pool' uuid: 7e66ba23-14c7-47b5-90fc-481ecc769138

Total devices 3 FS bytes used 888.04GiB
devid    1 size 931.51GiB used 738.03GiB path /dev/sdb
devid    2 size 465.76GiB used 228.00GiB path /dev/sdc
devid    5 size 1.82TiB used 966.03GiB path /dev/sdd

btrfs-progs v4.3
Data, RAID1: total=939.00GiB, used=871.94GiB
System, RAID1: total=32.00MiB, used=192.00KiB
Metadata, RAID1: total=27.00GiB, used=16.10GiB
GlobalReserve, single: total=512.00MiB, used=0.00B

I was planning to replace devid 2 with another larger HDD so that I can
have more space.
Because I have no spare slots for a new device, I have to firstly delete
the devid 2 and then add the new device to it. A simple calculation
suggested that after deleting devid 2, I should still have enough space
to hold a raid1 on the remaining 2 devices.

So I issued `btrfs device delete /dev/sdc /pool`, and after a while, my
FS turned write-only with this error in dmesg:
https://cfp.vim-cn.com/ccm2

I have reboot and tried for several times, and it will always stopped
with this kind of situation.
The last time I tried, the system refused to mount the btrfs array with
an error says something like:
`BTRFS: open_ctree failed`. I reboot forcefully and it mounted again.

Now I am afraid to try again, so I bring it here. I have 2 questions:
1. Do I have enough space to hold raid1 even if I deleted devid 2?
2. How to delete devid 2 safely?

About my system version:
Linux yang-z800 4.2.5-1-ARCH #1 SMP PREEMPT Tue Oct 27 08:13:28 CET 2015
x86_64 GNU/Linux
btrfs-progs v4.3.1

Thank you

-- 
Jiachen Yang 楊嘉晨
Graduate School of Information Science and Technology, Osaka University
Blog: https://farseerfc.me/
Gmail: farseerfc@gmail.com


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