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From: Kevin Corry <corryk@us.ibm.com>
Organization: IBM
To: Jens Axboe <axboe@suse.de>, Joe Thornber <joe@fib011235813.fsnet.co.uk>
Subject: Re: [linux-lvm] Re: [PATCH] 2.5 version of device mapper submission
Date: Tue, 15 Oct 2002 10:06:09 -0500
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On Tuesday 15 October 2002 09:52, Kevin Corry wrote:
> Also, am I correct in assuming that for merge_bvec_fn() to work properly, a
> driver's merge_bvec_fn() must also call the merge_bvec_fn() of the driver
> below it? For example, lets say we have a DM linear device that maps to two
> underlying devices (or in LVM-speak, a linear LV that spans two PVs), both
> of which are MD RAID-1 devices. For a given large request, DM may decide
> that it is fully contained within one of its two target devices, and allow
> all the requested pages to be added to the bio. However, it also needs to
> ask MD what its limits are for that request, or MD would still have to go
> through the trouble to split up the bio after it has been submitted.

This example actually should have been RAID-0 (striping), not RAID-1 
(mirroring). Sorry if this caused any confusion.

-- 
Kevin Corry
corryk@us.ibm.com
http://evms.sourceforge.net/