[stgt] tgt backend driver for Ceph block devices (rbd)

FUJITA Tomonori fujita.tomonori at lab.ntt.co.jp
Fri Jan 18 17:29:42 CET 2013

On Wed, 16 Jan 2013 18:47:14 -0800
Dan Mick <dan.mick at inktank.com> wrote:

> Hi, all.  I recently hacked at bs_rdwr and made it work as a
> proof-of-concept driver allowing tgt to be backed by the Ceph[1]
> storage cluster's RADOS block device (rbd)[2].  I thought I'd share
> the results of my investigations, as it's useful even in its current
> form:

Sounds interesting. If you send a patch, I'm happy to review and merge

> http://github.com/dmick/tgt, forked from http://github.com/fujita/tgt
> branch bs_rbd (https://github.com/dmick/tgt/tree/bs_rbd)
> This is a simple transliteration of bs_rdwr to use librbd/librados
> calls instead of normal file I/O calls (so might be instructive to
> diff bs_rbd.c against bs_rdwr.c to see what was involved).  It
> currently uses only the synchronous librbd interfaces, so each tgtd
> worker thread will block for completion of each request.  See the

That's fine. I/O worker threads are supposed to handle such
synchronous API (bs_rwdr.c use read/write system calls with O_SYNC).

If rdb provides the async API and it's preferable, then you don't need
to use I/O worker threads like bs_aio.c

> I was quite impressed at how easy this was, and how well-organized the
> stgt source is.  Kudos to the developers and maintainers!

Thanks ;)
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