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Re: [Xen-devel] [PATCH] libxl: prefer qdisk over blktap when choosing disk backend

Il 28/08/2013 12:59, George Dunlap ha scritto:
On Wed, Aug 28, 2013 at 11:35 AM, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote:
Wei Liu writes ("Re: [PATCH] libxl: prefer qdisk over blktap when choosing disk 
On Tue, Aug 27, 2013 at 03:22:43PM +0100, Wei Liu wrote:
There are some disk formats commonly supported by both qdisk and blktap.
As qdisk is better supported and blktap is unmaintained, we choose qdisk
over blktap whenever possible.
The reason for this ordering was that most kernels nowdays don't have
blktap.  So you don't get blktap on new systems, only on old ones.
That's good for stability I think.

Does that make any kind of sense ?
I don't think the original reasoning makes sense.  On systems without
blktap, the order of blktap / qdisk doesn't matter in the slightest.
The order only matters on old systems, with blktap; and there it's
better to use qdisk if possible, because it's maintained and blktap


I think is good prefer qdisk also for significant performance increase in comparison with blktap2. On attachment one benchmark about qdisk and blktap2 of previous month on windows 7 domU. I used only qdisk on my test system for one month without found bugs for now. Blktap is used only with xen, qdisk also with other softwares using qemu, is more supported/tested. I think is better point to upstream software and/or software used also by other opensource project for have optimize the development / testing and then have a final solution as best quality, performance and reliability. A good example are moved to upstream kernel and qemu (qemu still not enough in my opinion, I think that major of developer/users are wasting too much time on traditional while the upstream is now little used and tested unfortunately). The only question that comes about this patch is about "the qemu traditional case", although I think it should be abandoned as soon as possible to point all to the upstream qemu.

Sorry for my bad english.

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