Re: ceph-disk improvements

[Loic Dachary <loic@dachary.org>]

Hi Ilya,

On 05/04/2016 11:26, Ilya Dryomov wrote:
> On Tue, Apr 5, 2016 at 10:30 AM, Sebastien Han <shan@redhat.com> wrote:
>> Wido, I just discussed that with Sam last week and it seems that
>> bcache allocates a minor of 1 when creating the device.
>> Sam ended up writing this:
>> https://yaple.net/2016/03/31/bcache-partitions-and-dkms/
>> The fix is not complex not sure why it is not part of bcache yet...
> 
> I think it's just that no one complained loud enough.
> 
>>
>> Not sure if it's ceph-disk's job to do all of this with bcache though...
>> We might need to check with the bache guys what are their plans about this.
>> If this will go through at some point we might just wait, if not we
>> could implement the partition trick on ceph-disk.
> 
> Making something like this go through shouldn't be a problem.  Sam's
> patch is a bit of quick hack though - it messes up bcache device IDs
> and also limits the number of partitions to 16.  Better to avoid
> another hard-coded constant, if possible.
> 
>     # ls -lh /dev/bcache*
>     brw-rw---- 1 root disk 254,  0 Mar 31 20:17 /dev/bcache0
>     brw-rw---- 1 root disk 254,  1 Mar 31 20:17 /dev/bcache0p1
>     brw-rw---- 1 root disk 254, 16 Mar 31 20:17 /dev/bcache16
>     brw-rw---- 1 root disk 254, 17 Mar 31 20:17 /dev/bcache16p1
>     brw-rw---- 1 root disk 254, 32 Mar 31 20:17 /dev/bcache32
>     brw-rw---- 1 root disk 254, 33 Mar 31 20:17 /dev/bcache32p1
> 
> We had to solve almost exactly this problem in rbd.  I can submit
> a patch for bcache if it helps ceph-disk in the long run.

It would help. Implementing a workaround in ceph-disk to compensate for the fact that bcache does not support partitioning feels much better when there is hope it will eventually be removed :-)

Cheers

> 
> Thanks,
> 
>                 Ilya
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-- 
Loïc Dachary, Artisan Logiciel Libre
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