Re: rbd-nbd 2T limit

[Mykola Golub <to.my.trociny@gmail.com>]

On Thu, Mar 09, 2017 at 09:14:53AM +0200, Henrik Korkuc wrote:
> On 17-03-09 05:38, Max Yehorov wrote:
> >I was reading through release notes for 10.2.6 and there was a ticket
> >
> >rbd: rbd-nbd: disallow mapping images >2TB in size (issue#17219,
> >pr#11870, Mykola Golub)
> >
> >default nbd block size is 1k, valid values are from 512 to PAGE_SIZE
> >
> >rbd_nbd.cc sets blocksize to 512 here:
> >https://github.com/ceph/ceph/blob/master/src/tools/rbd_nbd/rbd-nbd.cc#L635
> >
> >Why 512 was chosen for rbd_nbd?
> >krbd also uses 512 sector size. Is there a reason to use 512 block
> >size vs 4k AF?
> I am also interested in >2TB NBD support and was disapointed when I couldn't
> mount 10TB images.
> 
> Based on issue in that commit for me it seems to be clear why it was done -
> some (most?) kernels in the wild do not support larger sizes. But it looks
> like support on unaffected kernels is already in master (not sure if it got
> backported to current releases). For reference:
> http://tracker.ceph.com/issues/17219 ->
> https://github.com/ceph/ceph/pull/11741 ->
> http://tracker.ceph.com/issues/18335 ->
> https://github.com/ceph/ceph/pull/13229

Yes, it removes the restriction for working kernels. It is going to be
backported to kraken and jewel:

http://tracker.ceph.com/issues/18910
http://tracker.ceph.com/issues/18911

-- 
Mykola Golub