Re: [Qemu-devel] [PATCH] hw: Add support for new LSI Logic devices.

[Hannes Reinecke]

On 09/13/2012 08:24 AM, Paolo Bonzini wrote:
> Il 12/09/2012 15:58, Anthony Liguori ha scritto:
> > Why would someone use this verses megasas vs. LSI vs virtio-scsi?
>
> LSI is dead.  Compare it to IDE.
>
> virtio-scsi has the highest performance, but it is not supported on all
> guests.  Compare it to virtio-blk.
>
> This vs. megasas is a good question; both can be compared to AHCI, they
> have good performance and have the advantage of compatibility with real
> hardware.  If this had gone in first, I would probably have rejected
> megasas, but this has the advantage of being used in VMware and
> VirtualBox.  Plus, unlike megasas Don said he'd work on SeaBIOS support,
> so it has further merit.
Ah.

Well, I'll be working on SeaBIOS support then, too :-)
I just haven't seen the need yet as it boots happily with an 
external ROM ...

However:
The main difference here is that the proposed 'lsilogic' controller 
emulates a SCSI or SAS controller, whereas the megasas emulates a 
RAID controller.
So for the former you have to implement _lot_ of code to make the 
emulation happy; most of which will be static (just look at the 
various config pages it'll has to implement) and just adds to the 
general size of the code without any functional benefit.

For megasas the controller itself does an emulation, which maps 
pretty well to qemu. And you don't have to implement all these 
transport-specific details.

Cheers,

Hannes
--
Dr. Hannes Reinecke                   zSeries & Storage
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