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

[Lukas Straub <lukasstraub2@web.de>]

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On Fri, 2 Apr 2021 22:46:25 +0200
Thomas <74cmonty@gmail.com> wrote:

> Hi,
> 
> I finished repartition of devices /dev/sda + /dev/sdb now.
> On both devices the first partition is equal in size:
> $ sudo fdisk -l /dev/sda
> Festplatte /dev/sda: 238,47 GiB, 256060514304 Bytes, 500118192 Sektoren
> Festplattenmodell: SanDisk SD8SBAT2
> Einheiten: Sektoren von 1 * 512 = 512 Bytes
> Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
> E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes
> Festplattenbezeichnungstyp: dos
> Festplattenbezeichner: 0x0914a19b
> 
> Gerät      Boot    Anfang      Ende  Sektoren Größe Kn Typ
> /dev/sda1            2048 497027071 497025024  237G 83 Linux
> /dev/sda2       497027072 500118191   3091120  1,5G 82 Linux Swap / Solaris
> 
> 
> $ sudo fdisk -l /dev/sdb
> Festplatte /dev/sdb: 238,47 GiB, 256060514304 Bytes, 500118192 Sektoren
> Festplattenmodell: SanDisk SD9TB8W2
> Einheiten: Sektoren von 1 * 512 = 512 Bytes
> Sektorgröße (logisch/physikalisch): 512 Bytes / 512 Bytes
> E/A-Größe (minimal/optimal): 512 Bytes / 512 Bytes
> Festplattenbezeichnungstyp: dos
> Festplattenbezeichner: 0xf23fc590
> 
> Gerät      Boot Anfang      Ende  Sektoren Größe Kn Typ
> /dev/sdb1         2048 497027071 497025024  237G 83 Linux
> 
> 
> However, the output of btrfs insp dump-s <device> is still different:
> $ sudo btrfs insp dump-s /dev/sda1 | grep dev_item.total_bytes
> dev_item.total_bytes    254476812288
> 
> $ sudo btrfs insp dump-s /dev/sdb1 | grep dev_item.total_bytes
> dev_item.total_bytes    256059465728

Interesting, this is again larger than the partition!
Did you actually run mkfs.btrfs after formating? Else it might still be
reading the old filesystem's superblock (just repartitioning does not
erase that).

> 
> Can you please advise how to fix this?
> My understanding is that size of btrfs superblock must be equal on both
> devices.

No, it's not a problem if the disks have different sizes. You have a
different problem here.

Regards,
Lukas Straub

> 
> THX
> 
> 
> Am 13.03.21 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.
> >
> >  
> 



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