Re: [Xen-users] Limited number of phy disks?

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Mon, Jan 19, 2009 at 12:34:15PM -0500, Dustin Henning wrote:
> OK, that post puts me in the minority, and I haven???t searched 
> or tested to verify this, but I thought the only problem with 
> SCSI emulation in Xen on HVMs was that the QEMU BIOS wouldn???t boot to a 
> SCSI drive.  
> My understanding is that the drives will be emulated, but you would 
> need drivers for them in order to use them.  I would also go as far as 
> to swear up and down that I have seen SCSI drivers for Xen HVMs more than 
> once (once they weren???t for HDs, but I think they were the other time).  
> Regardless, emulating SCSI shouldn't provide any performance increase once 
> using PV drivers anyway.

Yep, PV drivers are the best choise. 

I just meant that if you're not able to use PV drivers for some reason then 
emulated SCSI should be faster than emulated IDE.

If Qemu BIOS can't boot from SCSI drives then that's obviously a problem..
and leaves IDE as an only choise HVM guests (without PV drivers). 

-- Pasi

> Dustin
> 
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Nick Couchman
> Sent: Monday, January 19, 2009 10:02
> To: pasik@xxxxxx
> Cc: christoffer@xxxxxxxxx; xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Limited number of phy disks?
> 
> As far as I know, the current Qemu implementation in Xen for HVM support does 
> not support SCSI.  As James pointed out, though, if you use the GPL PV 
> drivers, you can assign as many devices as you want to the HVM domU.  The 
> catch to that is that if you ever have to boot with /nogplpv (to disable the 
> GPL PV drivers), you'll lose everything except disk devices hda-hdd.
> 
> -Nick
> 
> 
> -----Original Message-----
> From: Pasi Kärkkäinen <pasik@xxxxxx>
> To: Nick Couchman <Nick.Couchman@xxxxxxxxx>
> Cc: christoffer@xxxxxxxxx, xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Limited number of phy disks?
> Date: Mon, 19 Jan 2009 16:03:43 +0200
> 
> On Sun, Jan 18, 2009 at 02:45:06PM -0700, Nick Couchman wrote:
> > I assume you're running as an HVM?  What version of Xen are you using?  
> > As far as I know, Xen only support IDE drives in HVM domUs, 
> > and it only supports a total of four drives - hda, hdb, hdc, and hdd.
> > 
> 
> Hi.
> 
> Afaik Qemu supports SCSI disk/adapter emulation nowadays too.. 
> SCSI disk support is not yet implemented in Xen (version of Qemu)? 
> 
> -- Pasi

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