btrfs device scan

btrfs device scan

[Victor Roetman]

I have a couple computers running 2.6.38
(Ubuntu Natty 2.6.38-8-generic), and on both of them
"btrfs device scan" comes back with nothing other than
"failed to read /dev/sr0"

One computer has a btrfs RAID-1 volume, and the other has two separate
btrfs filesystems. The results are the same whether the filesystems are
mounted or not.

Why is "btrfs device scan" not scanning the devices?

vic

Re: btrfs device scan

[Helmut Hullen]

Hallo, Victor,

Du meintest am 12.05.11:

> I have a couple computers running 2.6.38
> (Ubuntu Natty 2.6.38-8-generic), and on both of them
> "btrfs device scan" comes back with nothing other than
> "failed to read /dev/sr0"

> One computer has a btrfs RAID-1 volume, and the other has two
> separate btrfs filesystems. The results are the same whether the
> filesystems are mounted or not.

What tells

        ls /dev/sd*
        ls /dev/md*

> Why is "btrfs device scan" not scanning the devices?

If I have understood the scan routine then it looks for all (?) block  
devices in "/dev".

Viele Gruesse!
Helmut

Re: btrfs device scan

[Victor Roetman]

On 05/12/2011 12:46 PM, Helmut Hullen wrote:
> Hallo, Victor,
> 
> Du meintest am 12.05.11:
> 
>> I have a couple computers running 2.6.38
>> (Ubuntu Natty 2.6.38-8-generic), and on both of them
>> "btrfs device scan" comes back with nothing other than
>> "failed to read /dev/sr0"
> 
> What tells
> 
>         ls /dev/sd*
>         ls /dev/md*

$ ls /dev/sd*
/dev/sda  /dev/sda1  /dev/sda2  /dev/sda5  /dev/sdb  /dev/sdb1  /dev/sdc
 /dev/sdc1

$ ls /dev/md*
ls: cannot access /dev/md*: No such file or directory

$ btrfs device scan
Scanning for Btrfs filesystems
failed to read /dev/sr0

$ btrfs filesystem show
failed to read /dev/sr0
Label: 'server-backup'  uuid: b927ead9-2e5b-4ee8-b9f4-7209177c49d8
	Total devices 2 FS bytes used 603.17GB
	devid    1 size 1.36TB used 605.28GB path /dev/sdb1
	devid    2 size 1.36TB used 605.26GB path /dev/sdc1

Btrfs Btrfs v0.19
$

Re: btrfs device scan

[Helmut Hullen]

Hallo, Victor,

Du meintest am 12.05.11:

>>> I have a couple computers running 2.6.38
>>> (Ubuntu Natty 2.6.38-8-generic), and on both of them
>>> "btrfs device scan" comes back with nothing other than
>>> "failed to read /dev/sr0"

[..]

> $ btrfs device scan
> Scanning for Btrfs filesystems
> failed to read /dev/sr0

That's a "well known" error; "scan" tries block devices which really  
cannot contain a btrfs filesystem.
People who don't use "udev" get a lot of more "failed to read" messages;  
"scan" seems to try every block device which exists in "/dev".

Maybe it's more reliable if "scan" doesn't look into "dev" but uses "/ 
proc/partitions".

> $ btrfs filesystem show
> failed to read /dev/sr0
> Label: 'server-backup'  uuid: b927ead9-2e5b-4ee8-b9f4-7209177c49d8
> 	Total devices 2 FS bytes used 603.17GB
> 	devid    1 size 1.36TB used 605.28GB path /dev/sdb1
> 	devid    2 size 1.36TB used 605.26GB path /dev/sdc1

That shows that (in this case) you can ignore the "scan" message.

Viele Gruesse!
Helmut

Re: btrfs device scan

[Arne Jansen]

On 12.05.2011 06:26, Victor Roetman wrote:
> I have a couple computers running 2.6.38
> (Ubuntu Natty 2.6.38-8-generic), and on both of them
> "btrfs device scan" comes back with nothing other than
> "failed to read /dev/sr0"
>
> One computer has a btrfs RAID-1 volume, and the other has two separate
> btrfs filesystems. The results are the same whether the filesystems are
> mounted or not.
>
> Why is "btrfs device scan" not scanning the devices?

Normally it does not report anything to stdout/stderr. You can see the
scan result in dmesg.

-Arne

>
> vic
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html