Re: [dm-devel] RFC: multipath IO multiplex

[Lars Marowsky-Bree <lmb novell com>]

On 2010-11-08T12:56:38, Alasdair G Kergon <agk redhat com> wrote:

> > I wonder how other latency-sensitive IO handles multipath? Maybe they
> > just haven't noticed yet they'd like a facility like this? ;-)
> As usual, it's the lack of a cancellation interface for incomplete I/O
> that seems to make the kernel-side option troublesome: we still have
> to wait for timeouts.

That would apply just as well to user-space though, no?

Like I said, the goal would be to report the first successful IO
completion, or the last failure - any other failures or results simply
get discarded at the kernel level. (Or wherever.)

> Do we prevent more than one I/O being sent in this mode, given that
> any other alternative would have races?

I don't follow. What races?

Of course the application needs to know this, and can't just treat it
like a regular block device.


Regards,
    Lars

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Architect Storage/HA, OPS Engineering, Novell, Inc.
SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde