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Date: Wed, 22 Dec 2010 14:27:10 +0100
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] scsi-generic and max request size
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To: Hannes Reinecke <hare@suse.de>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, ronnie sahlberg <ronniesahlberg@gmail.com>

On Wed, Dec 22, 2010 at 02:54:54PM +0100, Hannes Reinecke wrote:
> Most modern HBAs are using separate codepaths for streaming/block I/O
> anyway,

That's not true at all.  Every normal HBA justs passes normal SCSI
commands to the SCSI targets.  It's just raid adapters that take special
commands, and the megaraid one is extremly special as it actually
emulates a few SCSI commands even in RAID mode, which almost no other
HBA does.  Strictly speaking we should not allow scsi-generic with
megaraid_sas, except for the separate passthrough channels that the real
hardware has for things like tape drives.

> However, since Alex Graf is facing similar problems with the AHCI HBA of
> his maybe we could retry again ...

AHCI is a ATA adapter, and should never be used with scsi-generic for
disks.  Only for the ATAPI-attached cdroms/tapes/etc it could be used,
although it's quite pointless.