Re: BTRFS error (device sda1): bdev /dev/sdb1 errs: wr 2702175, rd 2719033, flush 0, corrupt 6, gen 0

[Thomas Schneider <74cmonty@gmail.com>]

Hello Chris,

many thanks for your analysis.

I'm not sure how to proceed in order to fix this error.
Obviously both devices, sda and sdb, are not partitioned 100% 
correct/optimal.

Therefore I consider to restart from scratch, means
- creating a file backup of OS
- deleting any partion on sda and sdb
- create 2 partitions on sda, part #1 for OS + part #2 for swap 
(swapfile is not working with BTRFS on multiple drives)
- restoring the (file) backup

Question:
Would you recommend to create a swap partition on sdb, too?

Regards
Thomas


Am 13.03.2021 um 19:02 schrieb Chris Murphy:
> On Sat, Mar 13, 2021 at 5:22 AM Thomas <74cmonty@gmail.com> wrote:
>
>> Gerät      Boot Anfang      Ende  Sektoren  Größe Kn Typ
>> /dev/sdb1         2048 496093750 496091703 236,6G 83 Linux
>> However the output of btrfs insp dump-s <device> is different:
>> thomas@pc1-desktop:~
>> $ sudo btrfs insp dump-s /dev/sdb1 | grep dev_item.total_bytes
>> dev_item.total_bytes    256059465728
> sdb1 has 253998951936 bytes which is *less* than the btrfs super block
> is saying it should be. 1.919 GiB less. I'm going to guess that the
> sdb1 partition was reduced without first shrinking the file system.
> The most common way this happens is not realizing that each member
> device of a btrfs file system must be separately shrunk. If you do not
> specify a devid, then devid 1 is assumed.
>
> man btrfs filesystem
> "The devid can be found in the output of btrfs filesystem show and
> defaults to 1 if not specified."
>
> I bet that the file system was shunk one time, this shrunk only devid
> 1 which is also /dev/sda1. But then both partitions were shrunk
> thereby truncating sdb1, resulting in these errors.
>
> If that's correct, you need to change the sdb1 partition back to its
> original size (matching the size of the sdb1 btrfs superblock). Scrub
> the file system so sdb1 can be repaired from any prior damage from the
> mistake. Shrink this devid to match the size of the other devid, and
> then change the partition.
>
>
>
>> Gerät      Boot    Anfang      Ende  Sektoren  Größe Kn Typ
>> /dev/sda1  *         2048 496093750 496091703 236,6G 83 Linux
>>
>> thomas@pc1-desktop:~
>> $ sudo btrfs insp dump-s /dev/sda1 | grep dev_item.total_bytes
>> dev_item.total_bytes    253998948352
> This is fine. The file system is 3584 bytes less than the partition.
> I'm not sure why it doesn't end on a 4KiB block boundary or why
> there's a gap before the start of sda2...but at least it's benign.
>
>