BTRFS scrub

[Jorge Fábregas]

Hi all,

I'm experimenting for the first time with btrfs on a scratch partition
and I wanted to test the scrub feature with:

#btrfs scrub start /btrfs

..but this is what I get when I check the status:

#btrfs scrub status /btrfs

scrub status for 543c5220-30ec-472b-a8ec-8c4c49f1fd32
	scrub started at Mon Jan 27 10:26:50 2014 and was aborted after 0 seconds
	total bytes scrubbed: 0.00 with 0 errors

I assume of course that checksums for data & metadata are enabled.  I
created the filesystem simply with:

# mkfs.btrfs /dev/sdc1

I'm not sure if I had to specify some option at creation time or if I
have to specify any at mount time (to enable the checksums).

Thanks for any help.

Regards,
Jorge

BTRFS scrub [SOLVED]

[Jorge Fábregas]

On 01/27/2014 10:35 AM, Jorge Fábregas wrote:
>  #btrfs scrub status /btrfs
>  
>  scrub status for 543c5220-30ec-472b-a8ec-8c4c49f1fd32
>  	scrub started at Mon Jan 27 10:26:50 2014 and was aborted after 0 seconds
>  	total bytes scrubbed: 0.00 with 0 errors 
Arrgh.  The filesystem was read-only.  I realized this when tried it with:

#btrfs scrub start /btrfs -B

..so that it doesn't run in the bacgrkound and that's where I got the
message about it being read-only.

-- 
Jorge

[Jorge Fábregas]

On 01/28/2014 02:43 PM, Chris Murphy wrote:
>  It can repair corrupt metadata however, since there are two copies. 
>  Same for Btrfs raid0, which by default uses data profile raid0 and
>  metadata profile raid1. 
Nice to know.  Thanks!

-- 
Jorge

[Chris Murphy]

On Jan 28, 2014, at 3:42 AM, Jorge Fábregas <jorge.fabregas(a)gmail.com&gt; wrote:
>  
>  I didn't know about read-only scrubs.  I guess I'll use that because, at
>  the moment, I'm just using one single disk and therefore btrfs can't fix
>  any corrupt block. 
It can repair corrupt metadata however, since there are two copies. Same for Btrfs raid0,
which by default uses data profile raid0 and metadata profile raid1.

Chris Murphy

[Jorge Fábregas]

On 01/27/2014 04:47 PM, Chris Murphy wrote:

>  Data and metadata checksums enabled with default mount options. 
>  They'd have to be explicitly disabled at mount time to not get them. 

Thanks Chris for confirming this.  I wasn't sure about it.


>  For scrubs that write corrections to disk, the volume needs to be
> mounted rw, and then:
>  
>  btrfs scrub start /mnt
>  
>  For read only scrubs you need -r flag to get useful information 
>  of what fixes would be done if they were enabled. This works
>  whether the device is mounted ro or rw.
>  
>  btrfs scrub start -r /mnt 
I didn't know about read-only scrubs.  I guess I'll use that because, at
the moment, I'm just using one single disk and therefore btrfs can't fix
any corrupt block.

Thanks!
Jorge

[Chris Murphy]

On Jan 27, 2014, at 7:35 AM, Jorge Fábregas <jorge.fabregas(a)gmail.com&gt; wrote:
>  
>  I assume of course that checksums for data & metadata are enabled.  I
>  created the filesystem simply with:
>  
>  # mkfs.btrfs /dev/sdc1
>  
>  I'm not sure if I had to specify some option at creation time or if I
>  have to specify any at mount time (to enable the checksums). 

Data and metadata checksums enabled with default mount options. They'd have to be
explicitly disabled at mount time to not get them. With a single device, data uses the
single profile so just one copy; metadata uses the DUP profile so two copies.

For scrubs that write corrections to disk, the volume needs to be mounted rw, and then:

btrfs scrub start /mnt

For read only scrubs you need -r flag to get useful information of what fixes would be
done if they were enabled. This works whether the device is mounted ro or rw.

btrfs scrub start -r /mnt


Chris Murphy