Re: [Qemu-devel] where can i customize rbd object size?

[Josh Durgin]

On 09/03/2015 09:48 AM, Stefan Hajnoczi wrote:
> On Wed, Aug 19, 2015 at 03:39:20PM +0800, Jaze Lee wrote:
> > Hello,
> >
> >      qemu-img convert -f qcow2 Trove---mysql-5.6---2015-07-16.qcow2 -O raw
> > rbd:openstack-00/8205d01a-874c-44c0-b114-1c03821fcc24:conf=/etc/ceph/ceph.conf
> >
> >     How can i specify the object size that rbd uses?  I found that the
> > qemu-image can only use the default object size. It is defined in
> > block/rbd.c
> >
> >      #define OBJ_MAX_SIZE
> > <https://lxr.missinglinkelectronics.com/qemu+v2.1.0/+code=OBJ_MAX_SIZE>
> > (1UL << OBJ_DEFAULT_OBJ_ORDER
> > <https://lxr.missinglinkelectronics.com/qemu+v2.1.0/+code=OBJ_DEFAULT_OBJ_ORDER>
> > )

Those are remnants from before librbd existed, they aren't used in qemu
anymore.

> >      If someone know how to specify the object size, please tell me. thanks
> > a lot.
> >      By the way i do not find the define for  OBJ_DEFAULT_OBJ_ORDER
> > <https://lxr.missinglinkelectronics.com/qemu+v2.1.0/+code=OBJ_DEFAULT_OBJ_ORDER>,
> > if someone knows , please tell me. Thanks a lot.
>
> I have CCed the rbd.c maintainer for you:
> $ scripts/get_maintainer.pl -f block/rbd.c
> Josh Durgin <address@hidden> (supporter:RBD)

Thanks for CCing me, I missed it before.

You can specify the rbd object size in bytes via the cluster_size
option, e.g.

qemu-img convert -f qcow2 Trove---mysql-5.6---2015-07-16.qcow2 -O raw -o 
cluster_size=8388608 
rbd:openstack-00/8205d01a-874c-44c0-b114-1c03821fcc24:conf=/etc/ceph/ceph.conf

The code handling this is here:

https://lxr.missinglinkelectronics.com/#qemu+v2.1.0/block/rbd.c#L318

Josh