reading an ex linux bcache disk

reading an ex linux bcache disk

[jdd]

Hello,

I have the following problem.

I used bcache on a computer with one hard drive and one small ssd.

(openSUSE 13.2)

this computer broke, it do not boot anymore. I could only recover the 
hard drive that seems perfectly working - I can read all the partitions 
but the bcache one.

is there any way to read the bcache partition content? As far as I know, 
the computer was shut down properly (it broke because somebody walked on 
it :-).

right now this is only a theoretical question (the problem is real, but 
there is nothing important on the bcache partition), but what I read on 
the net let me think this is not a trivial thing. If the disk content 
can't be recovered, I wont anymore use bcache :-(.

right now I get a "file system unknown" when I try to mount the bcache 
partition.

thanks for your help
jdd

Re: reading an ex linux bcache disk

[jdd]

Le 28/05/2015 09:31, Josep Lladonosa a écrit :

>  > right now I get a "file system unknown" when I try to mount the
> bcache partition.
>
> To mount a bcache partition you need an associated caching device
> (previous ssd, or a newly created), if I am not wrong. At least I had to
> do this to access to one.

could I use (for a moment only) an usb device? it's not for performance, 
only to access the partition. It seems to be possible for new install?

thanks
jdd

Re: reading an ex linux bcache disk

[Pavel Goran]

Hello jdd,

Thursday, May 28, 2015, 1:08:21 PM, you wrote:

> Hello,

> I have the following problem.

> I used bcache on a computer with one hard drive and one small ssd.

> (openSUSE 13.2)

> this computer broke, it do not boot anymore. I could only recover the 
> hard drive that seems perfectly working - I can read all the partitions 
> but the bcache one.

> is there any way to read the bcache partition content? As far as I know, 
> the computer was shut down properly (it broke because somebody walked on 
> it :-).

You  can  access  the  contents  of  the  bcache  volume without using a cache
partition  at all. All you'll need is a kernel that supports bcache and one or
two  commands  from  the  terminal.  I don't have time to go into details, but
probably it will be something like:

echo 1 > /sys/block/sda/sda3/bcache/running

(Taken  from https://wiki.archlinux.org/index.php/Bcache, you may want to look
there   or  at  https://www.kernel.org/doc/Documentation/bcache.txt  for  more
information.)

Pavel Goran
  

Re: reading an ex linux bcache disk

[jdd]

Le 28/05/2015 11:09, Pavel Goran a écrit :

> You  can  access  the  contents  of  the  bcache  volume without using a cache
> partition  at all. All you'll need is a kernel that supports bcache and one or
> two  commands  from  the  terminal.

good, because I can't ake the install of bcahe work with the old disk :-(

  I don't have time to go into details, but
> probably it will be something like:
>
> echo 1 > /sys/block/sda/sda3/bcache/running
>
> (Taken  from https://wiki.archlinux.org/index.php/Bcache, you may want to look
> there   or  at  https://www.kernel.org/doc/Documentation/bcache.txt  for  more
> information.)

I will read this now
thanks
jdd

Re: reading an ex linux bcache disk

[jdd]

Le 28/05/2015 11:09, Pavel Goran a écrit :

got it!

> echo 1 > /sys/block/sda/sda3/bcache/running

was the key :-)! thanks!

the manual says:

"make-bcache has the ability to format multiple devices at the same time"

but then:

To get started:

   mkfs.ext4 /dev/bcache0

so the word "format" is not used always with the same meaning (for me, 
formatting is creating a file system).

gladfully, make-bcache do *not* format the partition :-)

What I did:

* install a new system elsewhere (same distro I used with bcache). 
kernel 3.16.7
install bcache-tools

make-bcache -B /dev/sda8 (the old bcache backing)

tried to find /sys/block/sda/bcache, but it do not exist. Your example 
made me think the manual lacked a level, it have to be 
sys/block/sda/sda8/bcache

echo 1 > /sys/block/sda/sda3/bcache/running

and then /dev/bcache0 shows up!

mount /dev/bcache0 /mnt allows me to access the files on the partition

so good, thanks!
jdd