Re: [Qemu-devel] [PATCH v4] sheepdog: selectable object size support

[Teruaki Ishizaki]

(2015/02/06 11:18), Liu Yuan wrote:
> On Wed, Feb 04, 2015 at 01:54:19PM +0900, Teruaki Ishizaki wrote:
> > (2015/02/02 15:52), Liu Yuan wrote:
> > > On Tue, Jan 27, 2015 at 05:35:27PM +0900, Teruaki Ishizaki wrote:
> > > > Previously, qemu block driver of sheepdog used hard-coded VDI object size.
> > > > This patch enables users to handle "block_size_shift" value for
> > > > calculating VDI object size.
> > > >
> > > > When you start qemu, you don't need to specify additional command option.
> > > >
> > > > But when you create the VDI which doesn't have default object size
> > > > with qemu-img command, you specify block_size_shift option.
> > > >
> > > > If you want to create a VDI of 8MB(1 << 23) object size,
> > > > you need to specify following command option.
> > > >
> > > >   # qemu-img create -o block_size_shift=23 sheepdog:test1 100M
> > >
> > > Is it possible to make this option more user friendly? such as
> > >
> > >   $ qemu-img create -o object_size=8M sheepdog:test 1G
> >
> > At first, I thought that the object_size was user friendly.
> > But, Sheepdog has already the value of block_size_shift
> > in the inode layout that means like object_size.
> >
> > 'object_size' doesn't always fit right in 'block_size_shift'.
> > On the other hands, 'block_size_shift' always fit right in
> > 'object_size'.
> >
> > I think that existing layout shouldn't be changed easily and
> > it seems that it is difficult for users to specify
> > the object_size value that fit right in 'block_size_shift'.
>
> I don't think we need to change the layout. block_size_shift is what QEMU talks
> to sheep, and QEMU options is what users talks to QEMU. We can convert the user
> friendly object size into block_size_shift internally in the driver before
> sending it tosheep daemon, no?
For example, users specify 12MB for object size, block_size_shift
doesn't fit exactly to an integer.

I suppose that normally an administrator do format sheepdog cluster
with specifying block_size_shift and users usually do qemu-img command
without a block_size_shift option.

I think that the block_size_shift option of qemu-img command is used
for a experimental purpose.

Thanks,
Teruaki Ishizaki