maximum size of a block device in a domU

maximum size of a block device in a domU

[Sebastian Reitenbach]

Hi,


I'm looking for an answer to my question that I have since days, but not 
found an answer yet. 
I am looking for the maximum size a block device, like a harddisk can have?
AFAIK, on vmware, there is a limit at 2TB for block devices of being usable?
I was already asking on the users list, and searched the archives, but did 
not found a sufficient answer yet, therefore I hope one of the developer 
will let me know.
Thanks.

kind regards
Sebastian

Re: maximum size of a block device in a domU

[Samuel Thibault]

Sebastian Reitenbach, le Mon 21 Jul 2008 12:48:51 +0200, a écrit :
> I'm looking for an answer to my question that I have since days, but not 
> found an answer yet. 
> I am looking for the maximum size a block device, like a harddisk can have?
> AFAIK, on vmware, there is a limit at 2TB for block devices of being usable?
> I was already asking on the users list, and searched the archives, but did 
> not found a sufficient answer yet, therefore I hope one of the developer 
> will let me know.

For HVM domU, since qemu supports lba48, the maximum should be 2^57B
there, not tested though :) The actual limit is then the size that dom0
itself can cope with.

For PV domU, the PV interface is 64bit, so theorically 2^73B...  Then
it's up to limitations of dom0 and domU themselves.

Samuel

Re: maximum size of a block device in a domU

[Sebastian Reitenbach]

Hi Samuel,

Samuel Thibault <samuel.thibault@eu.citrix.com> wrote:
> Sebastian Reitenbach, le Mon 21 Jul 2008 12:48:51 +0200, a écrit :
> > I'm looking for an answer to my question that I have since days, but not
> > found an answer yet.
> > I am looking for the maximum size a block device, like a harddisk can
have?
> > AFAIK, on vmware, there is a limit at 2TB for block devices of being
usable?
> > I was already asking on the users list, and searched the archives, but
did
> > not found a sufficient answer yet, therefore I hope one of the developer
> > will let me know.
>
> For HVM domU, since qemu supports lba48, the maximum should be 2^57B
> there, not tested though :) The actual limit is then the size that dom0
> itself can cope with.
>
> For PV domU, the PV interface is 64bit, so theorically 2^73B...  Then
> it's up to limitations of dom0 and domU themselves.

Thanks a lot for the fast and informative answer.

Sebastian

RE: maximum size of a block device in a domU

[Jayaraman, Bhaskar]

Hi, if I were using Xen 3.2.1 and above and if I were to direct assign a block device to a HVM guest will I still play by the rules mentioned below for maximum size of the device?
Regards,
Bhaskar.

-----Original Message-----
From: xen-devel-bounces@lists.xensource.com [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Sebastian Reitenbach
Sent: Monday, July 21, 2008 5:00 PM
To: samuel.thibault@eu.citrix.com
Cc: xen-devel@lists.xensource.com
Subject: Re: [Xen-devel] maximum size of a block device in a domU

Hi Samuel,

Samuel Thibault <samuel.thibault@eu.citrix.com> wrote:
> Sebastian Reitenbach, le Mon 21 Jul 2008 12:48:51 +0200, a écrit :
> > I'm looking for an answer to my question that I have since days, but not
> > found an answer yet.
> > I am looking for the maximum size a block device, like a harddisk can
have?
> > AFAIK, on vmware, there is a limit at 2TB for block devices of being
usable?
> > I was already asking on the users list, and searched the archives, but
did
> > not found a sufficient answer yet, therefore I hope one of the developer
> > will let me know.
>
> For HVM domU, since qemu supports lba48, the maximum should be 2^57B
> there, not tested though :) The actual limit is then the size that dom0
> itself can cope with.
>
> For PV domU, the PV interface is 64bit, so theorically 2^73B...  Then
> it's up to limitations of dom0 and domU themselves.

Thanks a lot for the fast and informative answer.

Sebastian


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Re: maximum size of a block device in a domU

[Samuel Thibault]

Jayaraman, Bhaskar, le Tue 22 Jul 2008 13:18:23 +0800, a écrit :
> Hi, if I were using Xen 3.2.1 and above and if I were to direct assign a block device to a HVM guest will I still play by the rules mentioned below for maximum size of the device?

If by "direct assign" you mean setting disk = [ 'phy:sda4,hda,w' ] in
the config file, then yes you are still going through the IDE emulation,
limited to 2^48 sectors, i.e. 2^57B, plus the dom0 limitations (and the
HVM domU limitations of course).

Samuel

RE: maximum size of a block device in a domU

[Jayaraman, Bhaskar]

Samuel, I was actually referring to the equivalent of dedicating a PCI HBA to a paravirtualized guest(using pciback) in an HVM guest. I believe this is possible with VT-d hardware and with the Xen 3.2.1 kernel for an HVM as well, although I haven't been able to do this myself yet to an HVM. In any case 2^57 is large enough for any domain to keep going for some time, with h/w dedicated or not.
Regards,
Bhaskar.

-----Original Message-----
From: Samuel Thibault [mailto:samuel.thibault@eu.citrix.com]
Sent: Tuesday, July 22, 2008 2:59 PM
To: Jayaraman, Bhaskar
Cc: Sebastian Reitenbach; xen-devel@lists.xensource.com
Subject: Re: [Xen-devel] maximum size of a block device in a domU

Jayaraman, Bhaskar, le Tue 22 Jul 2008 13:18:23 +0800, a écrit :
> Hi, if I were using Xen 3.2.1 and above and if I were to direct assign a block device to a HVM guest will I still play by the rules mentioned below for maximum size of the device?

If by "direct assign" you mean setting disk = [ 'phy:sda4,hda,w' ] in
the config file, then yes you are still going through the IDE emulation,
limited to 2^48 sectors, i.e. 2^57B, plus the dom0 limitations (and the
HVM domU limitations of course).

Samuel

Re: maximum size of a block device in a domU

[Samuel Thibault]

Jayaraman, Bhaskar, le Tue 22 Jul 2008 20:14:01 +0800, a écrit :
> I was actually referring to the equivalent of dedicating a PCI HBA to a paravirtualized guest(using pciback) in an HVM guest.

Ok, then there shouldn't be any limit.

Samuel