Re: BTRFS over LVM remounts read-only

[Hugo Mills <hugo@carfax.org.uk>]

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On Sat, Jan 11, 2014 at 03:32:26PM +0100, MegaBrutal wrote:
> Hello,
> 
> I'm using BTRFS over LVM and after some time of usage (days or hours),
> it just remounts itself, and I don't see the reason why, while it is
> said to be fault-tolerant.
> 
> It is possible that I have bad sectors on the disk, though I don't
> find it likely. Even then, I don't think bad sectors should cause that
> much of a problem that the FS needs to be remounted because of it. Is
> there a way to make BTRFS to detect and mark bad sectors like any
> other file system does?
> 
> Here are the /etc/fstab entries those concern my BTRFS file system:
> /dev/mapper/vmhost--vg-vmhost--rootfs /               btrfs
> defaults,subvol=@ 0       1
> /dev/mapper/vmhost--vg-vmhost--rootfs /home           btrfs
> defaults,subvol=@home 0       2
> /dev/mapper/vmhost--vg-vmhost--rootfs /media/btrfs    btrfs   noauto
>          0       3
> 
> I've attached a dmesg output that may help developers to see what's the problem.
> 
> Do you have any ideas what causes the problem?

[60631.481913] attempt to access beyond end of device
[60631.481935] dm-1: rw=1073, want=42917896, limit=42917888
[60631.481941] btrfs_dev_stat_print_on_error: 34 callbacks suppressed
[60631.481949] btrfs: bdev /dev/mapper/vmhost--vg-vmhost--rootfs errs: wr 311347, rd 0, flush 0, corrupt 0, gen 0

   This is the problem.

   It looks like you've shrunk the LV without first shrinking the
filesystem. Depending on how much you shrunk it by, the odds are
fairly good that significant chunks of the FS are now toast.

   Hugo.

> Also, if the disaster happens and the FS gets remounted read-only, is
> there a way to force remount it in read-write mode? I've tried "mount
> -o remount,rw" and "mount -o force,remount,rw" too, but it doesn't
> work. Also I can't mount the BTRFS root or any subvolumes elsewhere
> until I restart the system.
> 
> Probably my description of the problem wasn't detailed enough, but
> since I'm totally clueless about the problem (not counting the
> possible bad sectors), I can't tell more right now. But you can ask
> more details and I'll try to answer.
> 
> 
> MegaBrutal



-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
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