btrfs raid1 degraded needs chunk root rebuild

DISCUSSION Vladi Gergov 1 participant 1 message Nov 17, 2016 Btrfs file system

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Vladi Gergov

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2016-11-17 22:08 UTC #0 lore raw

Any ideas if currently I can still recover data from this volume? I have tried the new btrfs tools with btrfs rescue chunk-recover without much success. Any ideas if i can recover any of the data?

----- Forwarded message from Chris Mason <[email protected]> -----

From: Chris Mason <[email protected]>
Subject: Re: btrfs raid1 degraded does not mount or fsck
To: Vladi Gergov <[email protected]>
Cc: linux-btrfs <[email protected]>
Date: Tue, 16 Nov 2010 16:50:58 -0500
User-Agent: Sup/git

Excerpts from Vladi Gergov's message of 2010-10-29 16:53:42 -0400:

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gypsyops @ /mnt > sudo mount -o degraded /dev/sdc das3/
Password:
mount: wrong fs type, bad option, bad superblock on /dev/sdc,
missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so

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[  684.577540] device label das4 devid 2 transid 107954 /dev/sdc
[  684.595150] btrfs: allowing degraded mounts
[  684.595594] btrfs: failed to read chunk root on sdb
[  684.604110] btrfs: open_ctree failed
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gypsyops @ /mnt > sudo btrfsck /dev/sdc
btrfsck: volumes.c:1367: btrfs_read_sys_array: Assertion `!(ret)' failed.

Ok, I dug through this and found the bug responsible for your unmountable FS. When we're mounted in degraded mode, and we don't have enough drives available to do raid1,10, we're can use the wrong raid level for new allocations.

I'm fixing the kernel side so this doesn't happen anymore, but I'll need to rebuild the chunk tree (and probably a few others) off your good disk to fix things.

I've got it reproduced here though, so I'll make an fsck that can scan for the correct trees and fix it for you.

Since you're basically going to be my first external fsck customer, is there anyway you can do a raw device based backup of the blocks? This way if I do mess things up we can repeat the experiment.

-chris

!DSPAM:4ce2fd55191821234852255!

----- End forwarded message -----

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