Scrub errors but no errors ?!?

Scrub errors but no errors ?!?

[Swâmi Petaramesh]

Hi,

Using kernel 3.19 on Ubuntu 15.04

I have a BTRFS Raid-1 FS made from 2 Luks-encrypted devices, each one built 
atop a bcache device.

The machine runs smoothly from this setup.

When I scrub said FS, it ends by spitting a message on console stating that 
"Scrub found errors but corrected them"

However if I then type :

# btrfs scrub stat /
scrub status for 53a35066-1a7b-4fe1-9f94-a923a7f9e3af
        scrub started at Sun Jun 28 11:17:50 2015 and finished after 30657 
seconds
        total bytes scrubbed: 3.01TiB with 0 errors

# btrfs dev stat /
[/dev/mapper/c_b].write_io_errs   0
[/dev/mapper/c_b].read_io_errs    0
[/dev/mapper/c_b].flush_io_errs   0
[/dev/mapper/c_b].corruption_errs 0
[/dev/mapper/c_b].generation_errs 0
[/dev/mapper/c_a].write_io_errs   0
[/dev/mapper/c_a].read_io_errs    0
[/dev/mapper/c_a].flush_io_errs   0
[/dev/mapper/c_a].corruption_errs 0
[/dev/mapper/c_a].generation_errs 0

...How comes ?

TIA for any insight.

-- 
Swâmi Petaramesh <swami@petaramesh.org> http://petaramesh.org PGP 9076E32E

Re: Scrub errors but no errors ?!?

[Duncan]

Swâmi Petaramesh posted on Mon, 29 Jun 2015 10:42:14 +0200 as excerpted:

> Using kernel 3.19 on Ubuntu 15.04
> 
> I have a BTRFS Raid-1 FS made from 2 Luks-encrypted devices, each one
> built atop a bcache device.
> 
> The machine runs smoothly from this setup.
> 
> When I scrub said FS, it ends by spitting a message on console stating
> that "Scrub found errors but corrected them"
> 
> However if I then type :
> 
> # btrfs scrub stat /
> scrub status for 53a35066-1a7b-4fe1-9f94-a923a7f9e3af
>         scrub started at Sun Jun 28 11:17:50 2015 and finished after
>         30657 seconds
>         total bytes scrubbed: 3.01TiB with 0 errors


FWIW, I've seeing (and wondering) the same thing, tho with newer kernel 
(v4.1.0) and userspace (also v4.1)

I'm running pair-device raid1 mode (both data/metadata) but one of the 
two devices is slowly relocating sectors, so I thought it /might/ be 
btrfs detecting some oddness due to that.

But if you're seeing it too, that's unlikely.  So indeed, what's this 
found errors and corrected them bit, with no errors shown as found?

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman