Converting existing partition to bcache backing device without loss of data

Converting existing partition to bcache backing device without loss of data

[Adam Brenner]

Howdy,

I am in the process of testing bcache on our HPC cluster to act as
cache for our gluster storage (~750TB).

I notice that during the setup process on our test cluster, our
backing device (where all our data is stored) will need to be
formatted in order to support bcache.

Does a way exist so we do not have to format our backing device? Or is
working being done to support this?

Thanks,
-Adam

--
Adam Brenner
Computer Science, Undergraduate Student
Donald Bren School of Information and Computer Sciences

Research Computing Support
Office of Information Technology
http://www.oit.uci.edu/rcs/

University of California, Irvine
www.ics.uci.edu/~aebrenne/
aebrenne-sXc7qaQca9o@public.gmane.org

Re: Converting existing partition to bcache backing device without loss of data

[Jason Warr]

On 08/08/2013 11:27 AM, Adam Brenner wrote:
> Howdy,
>
> I am in the process of testing bcache on our HPC cluster to act as
> cache for our gluster storage (~750TB).
>
> I notice that during the setup process on our test cluster, our
> backing device (where all our data is stored) will need to be
> formatted in order to support bcache.
You can't convert an in use block device into a backing store. 

Your best bet is to replace your gluster bricks either one at a time or
in acceptable groups with bricks that are bcache backed.

But without knowing more about how your gluster setup is architect-ed
this is just a guess.
> Does a way exist so we do not have to format our backing device? Or is
> working being done to support this?
In your particular case converting in place is not likely a very good
method even if it were supported.  Gluster is designed to be flexible in
such a way that you can replace existing storage bricks with new and
improved bcache backed bricks by simply replacing a replica in a set.
>
> Thanks,
> -Adam
>
> --
> Adam Brenner
> Computer Science, Undergraduate Student
> Donald Bren School of Information and Computer Sciences
>
> Research Computing Support
> Office of Information Technology
> http://www.oit.uci.edu/rcs/
>
> University of California, Irvine
> www.ics.uci.edu/~aebrenne/
> aebrenne-sXc7qaQca9o@public.gmane.org
> --
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Re: Converting existing partition to bcache backing device without loss of data

[Kent Overstreet]

On Thu, Aug 08, 2013 at 09:27:33AM -0700, Adam Brenner wrote:
> Howdy,
> 
> I am in the process of testing bcache on our HPC cluster to act as
> cache for our gluster storage (~750TB).
> 
> I notice that during the setup process on our test cluster, our
> backing device (where all our data is stored) will need to be
> formatted in order to support bcache.
> 
> Does a way exist so we do not have to format our backing device? Or is
> working being done to support this?

Unfortunately, there's no general purpose way - the faq explains why (I
just fixed the wiki so it's there again :)

http://bcache.evilpiepirate.org/FAQ/

However, Gabriel de Perthuis has a tool to do in place conversion - I
can't remember if it was limited to lvm devices or not - Gabriel, what
was the link to that again? I should stick a link to it in the wiki or
give you an account on it so you can.

Re: Converting existing partition to bcache backing device without loss of data

[Gabriel de Perthuis]

ven. 09 août 2013 02:36:57 CEST, Kent Overstreet a écrit :
> On Thu, Aug 08, 2013 at 09:27:33AM -0700, Adam Brenner wrote:
>> Howdy,
>>
>> I am in the process of testing bcache on our HPC cluster to act as
>> cache for our gluster storage (~750TB).
>>
>> I notice that during the setup process on our test cluster, our
>> backing device (where all our data is stored) will need to be
>> formatted in order to support bcache.
>>
>> Does a way exist so we do not have to format our backing device? Or is
>> working being done to support this?
>
> Unfortunately, there's no general purpose way - the faq explains why (I
> just fixed the wiki so it's there again :)
>
> http://bcache.evilpiepirate.org/FAQ/
>
> However, Gabriel de Perthuis has a tool to do in place conversion - I
> can't remember if it was limited to lvm devices or not - Gabriel, what
> was the link to that again? I should stick a link to it in the wiki or
> give you an account on it so you can.

Yup, here is my conversion tool: https://github.com/g2p/blocks

I've added it to the FAQ.