pass-through disk

John

unread,

Oct 29, 2008, 1:29:03 PM10/29/08

to

Hi all,

With Windows 2008 hyper-V, when should we consider using pass-through disk?

thank you!

Charlie Russel - MVP

unread,

Oct 29, 2008, 2:49:14 PM10/29/08

to

Never?

Seriously, the speed differential between fixed disks and passthrough is
pretty small. And you lose any ability to leverage the advantages of VHD, or
VSS support, etc. But if absolute speed is essential, and you have an
application such as SQL Server that will directly manage the disks, then it
might make sense. But I won't be using them at all.

--
Charlie.
http://msmvps.com/blogs/xperts64
http://mvp.support.microsoft.com/profile/charlie.russel

"John" <Jo...@discussions.microsoft.com> wrote in message
news:67FE32FE-0BED-42DD...@microsoft.com...

John

unread,

Oct 29, 2008, 4:58:00 PM10/29/08

to

Thank you and thank you.

The general rule for Hyper-V VM highly available is per VM per LUN.

What about VM with lots of drive letters and should we assign more LUNs to
it?

Paul Weterings

unread,

Oct 30, 2008, 9:13:47 AM10/30/08

to

Charlie Russel - MVP wrote:

> Never?
>
> Seriously, the speed differential between fixed disks and passthrough is
> pretty small. And you lose any ability to leverage the advantages of
> VHD, or VSS support, etc. But if absolute speed is essential, and you
> have an application such as SQL Server that will directly manage the
> disks, then it might make sense. But I won't be using them at all.
>
>

As Charlie mentions, there seems to be little performance difference. I
have not tested this myself yet, for me it's only hearsay. Did you do
tests yet Charlie?

However, the Exchange guys say this:

[quote]
We recommend using SCSI pass-through storage to host transport and
mailbox databases and transaction log files. Although using pass-through
disks limits the portability of virtual machines, this configuration has
shown to provide the best performance of all storage options for a
virtualized Exchange server.
[/quote]

--

/ ) Regards,
/ /_________
_|__|__) Paul Weterings
/ (O_) http://www.servercare.nl
__/ (O_)
____(O_)

Charlie Russel - MVP

unread,

Oct 30, 2008, 7:06:20 PM10/30/08

to

If you need a drive letter, you should assign a LUN to it, IMHO.

--
Charlie.
http://msmvps.com/blogs/xperts64
http://mvp.support.microsoft.com/profile/charlie.russel

"John" <Jo...@discussions.microsoft.com> wrote in message

news:3D0F453E-8B1D-4A00...@microsoft.com...

Charlie Russel - MVP

unread,

Oct 30, 2008, 7:05:38 PM10/30/08

to

No personal tests (my use is very different, and I almost always use
expanding disks). But this was as reported by the product team at the launch
event in Bellevue. I don't remember the number, but it was in the single
digits of percentage, at best.

--
Charlie.
http://msmvps.com/blogs/xperts64
http://mvp.support.microsoft.com/profile/charlie.russel

"Paul Weterings" <Paul-nospam-@syncpuls-dot-com> wrote in message
news:4909b30b$0$16196$e4fe...@dreader25.news.xs4all.nl...

Kurt Roggen [BE]

unread,

Nov 12, 2008, 6:34:59 PM11/12/08

to

I can confirm what Charlie says.... This is feedback from Jeff Woolsey (PM
HyperV).
So it is not really a performance issue is it really a portability issue.
At Microsoft, 1 criteria for choosing between pass-through and (fixed) .vhd
is the size! (MS uset s 300 GB)
Do you really want more than 300 GB of data living in a .VHD??
Sure, 300 GB is probably different for most of us, but you get the idea,
right!

Hope this helps!
--
Kurt Roggen [BE] - MVP
http://trycatch.be/blogs/roggenk

"Charlie Russel - MVP" <cha...@mvKILLALLSPAMMERSps.org> wrote in message
news:ONWYHQuO...@TK2MSFTNGP04.phx.gbl...