On Fri, Sep 12, 2008 at 8:16 PM, Kiyoshi Ueda <[email protected]> wrote:
> This patch enables request-based dm.
>
> o Request-based dm and bio-based dm coexist, since there are
> some target drivers which are more fitting to bio-based dm.
> Also, there are other bio-based devices in the kernel
> (e.g. md, loop).
> Since bio-based device can't receive struct request,
> there are some limitations on device stacking between
> bio-based and request-based.
>
> type of underlying device
> bio-based requeset-based
> ----------------------------------------------
> bio-based OK OK
> request-based NG OK
>
So will some configurations would become impossible, if a target is
made request-based and bio-based one is removed. Hope both
types of targets would co-exist and would be selectable for sometime.
> The device type is recognized by the queue flag in the kernel,
> so dm follows that.
>
> o The type of a dm device is decided at the first table loading time.
> Until then, mempool creations are deferred, since mempools for
> request-based dm are different from those for bio-based dm.
> Once the type of a dm device is decided, the type can't be changed.
>
> o Currently, request-based dm supports only tables that have a single
> target.
Barrier support should be straight forward?
Thanks
Nikanth Karthikesan
Hi Nikanth,
On Fri, 24 Oct 2008 13:22:46 +0530, "Nikanth K" wrote:
> On Fri, Sep 12, 2008 at 8:16 PM, Kiyoshi Ueda wrote:
> > This patch enables request-based dm.
> >
> > o Request-based dm and bio-based dm coexist, since there are
> > some target drivers which are more fitting to bio-based dm.
> > Also, there are other bio-based devices in the kernel
> > (e.g. md, loop).
> > Since bio-based device can't receive struct request,
> > there are some limitations on device stacking between
> > bio-based and request-based.
> >
> > type of underlying device
> > bio-based requeset-based
> > ----------------------------------------------
> > bio-based OK OK
> > request-based NG OK
> >
>
> So will some configurations would become impossible, if a target is
> made request-based and bio-based one is removed. Hope both
> types of targets would co-exist and would be selectable for sometime.
If the target is used anywhere in the device stack (e.g. linear),
both types of the target are needed, and that is possible.
As for multipath, see my another reply to your comment for PATCH 13.
Thanks,
Kiyoshi Ueda