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Changing the locations of Base Drives in Virtual Server

Source: microsoft.public.virtualserver
Sent: 06/04/2007
From: Mezz <(email address - cut out)>
Message:

Greetings to all,

I've got a three tiered VHD. Its got a thin differencing drive on top
(vhd2), a middle layer parent/base vhd (vhd1), and a Base Vhd
(basevhd).

What I'd like to do is move the base VHD and actually make that top
layer a valid, startable vhd.

However, whenever I, though the administrators page, change the
location of that base drive, the middle layer vhd (vhd1) is valid,
however, after that, the top level drive (vhd2) is invalid.

When attempting to change the location of the base drive through the
COM interface, I get the same effect. The top level drive always ends
up unusable.

I understand that this is probably due to the timestamp between the
top level drive and the middle lvl drive changing when I reattach the
base to the middle layer. The event viewer seems to confirm this,
where I see the message:

The parent virtual hard disk appears to have been modified without
using the differencing virtual hard disk located at "vhd2's path".
Modifying the parent virtual hard disk may result in data corruption.
It is strongly recommended that you lock the parent virtual hard disk
to prevent this in the future. If you recently changed time zones on
your computer, you can safely continue using this virtual hard disk.

So, after that, here is the question.
What is the way to continue safely using the virtual hard disk? I
haven't found anything in the admin pages to make this drive valid
again. In fact, the only way I've found of using the drive again is
starting up the machine in VPC, which seems to treat that same error
as a warning, instead of a showstopper. VPC then apparently resynchs
the timestamps of the parent and differencing drives.

Of course, the best of all possible worlds would be a scripted way
that I can actually set the location of this base drive without
invalidating the top level drive, but a way of suppressing the 'parent
disk modification' error would also work (in a hacky way).

Any experience with this out there?

Is there a way to get around this issue in Virtual Server?

Thanks,
-Mezz

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Related Messages

Re: Changing the locations of Base Drives in Virtual Server

Sent: 06/04/2007
From: Mezz <(email address - cut out)>
Message:

I neglected to mention the version of VS I'm using:
Microsoft=AE Virtual Server 2005 R2 Service Pack 1 (SP1)
I believe this is the RC. I fetched it a few weeks back.
-Mezz

Re: Changing the locations of Base Drives in Virtual Server

Sent: 06/04/2007
From: Richard Cardona <(email address - cut out)>
Message:

Virtual Server Undo (VUDs) and Differencing Disks (VHDs) have two paths
to their parent disks, a relative and an absolute path. One of these
paths has to be valid for Virtual Server to open the disk chain and the
timestamp of the Parent is kept in differencing disk to warn you of changes.

When you say you're using the Administrator's page to change the
location of a base drive you talking about using "Inspect Disk" to
update every disk in the differencing chain? This should always be able
to work. The equivalent in COM API is to update the VMHardDisk.Parent
member of each differencing disk until you reach the base.

If you are only updating the middle VHD the leaf or middle VHD that may
not be enough.

Secondly, Microsoft has openly published the VHD specification. As an
exercise I wrote a simple, private inspector to dump the VHD headers and
for the high-change environments I work with and update paths inside of
VHDs. There are four paths actually, two relative, two absolute in
single-byte and Unicode in VHDs. Updating them requires updating
timestamps and the header checksums. If you do everything right,
Virtual Server will not complain.

Using the spec, is a bit extreme but you should be able to accomplish
everything with the COM APIs.

Richard

Mezz wrote:

Show quoted text

> Greetings to all,
>
> I've got a three tiered VHD. Its got a thin differencing drive on top
> (vhd2), a middle layer parent/base vhd (vhd1), and a Base Vhd
> (basevhd).
>
> What I'd like to do is move the base VHD and actually make that top
> layer a valid, startable vhd.
>
> However, whenever I, though the administrators page, change the
> location of that base drive, the middle layer vhd (vhd1) is valid,
> however, after that, the top level drive (vhd2) is invalid.
>
> When attempting to change the location of the base drive through the
> COM interface, I get the same effect. The top level drive always ends
> up unusable.
>
> I understand that this is probably due to the timestamp between the
> top level drive and the middle lvl drive changing when I reattach the
> base to the middle layer. The event viewer seems to confirm this,
> where I see the message:
>
> The parent virtual hard disk appears to have been modified without
> using the differencing virtual hard disk located at "vhd2's path".
> Modifying the parent virtual hard disk may result in data corruption.
> It is strongly recommended that you lock the parent virtual hard disk
> to prevent this in the future. If you recently changed time zones on
> your computer, you can safely continue using this virtual hard disk.
>
> So, after that, here is the question.
> What is the way to continue safely using the virtual hard disk? I
> haven't found anything in the admin pages to make this drive valid
> again. In fact, the only way I've found of using the drive again is
> starting up the machine in VPC, which seems to treat that same error
> as a warning, instead of a showstopper. VPC then apparently resynchs
> the timestamps of the parent and differencing drives.
>
> Of course, the best of all possible worlds would be a scripted way
> that I can actually set the location of this base drive without
> invalidating the top level drive, but a way of suppressing the 'parent
> disk modification' error would also work (in a hacky way).
>
> Any experience with this out there?
>
> Is there a way to get around this issue in Virtual Server?
>
> Thanks,
> -Mezz
>

Re: Changing the locations of Base Drives in Virtual Server

Sent: 06/04/2007
From: Richard Cardona <(email address - cut out)>
Message:

Mezz wrote:

In addition to updating VHD paths in Differencing disks, for the
top-level VHD bound a to VM with Undo disks enabled, Virtual Server
keeps track of the path to the parent of VUD in the .vmc configuration
file - even though that data is redundantly stored in the VUD itself.

If you ever need to move the parent of a VUD file you have to update the
configuration information in the vmc for it to continue to work.

Show quoted text

> I neglected to mention the version of VS I'm using:
> Microsoft® Virtual Server 2005 R2 Service Pack 1 (SP1)
> I believe this is the RC. I fetched it a few weeks back.
> -Mezz

Re: Changing the locations of Base Drives in Virtual Server

Sent: 06/04/2007
From: Mezz <(email address - cut out)>
Message:

Thanks for the response, Richard.
I've currently got a VM, same as the scenario I've described above.
Its in perfect, happy working order, and I am able to start it. It
currently has no vuds associated with it.

Here's what I do.

1) Inspect the top level VHD: The vhd, and the two bases show
correctly.
2) Move the base image from C:\Bases to C:\Bases\NewBaseFolder
3) Refresh the inspection page: In the inspection page, the middle
parent drive shows up correctly, however, where the base drive link
was shown before, I now see the message

'The virtual hard disk file "C:\Bases\Basea.vhd" is in use by
another process. Click here to update it.'

I suppose that's might be another way of telling us that it can't find
it. So far so good.

4) Click the 'The virtual hard disk file "C:\Bases\Basea.vhd" is in
use by another process. Click here to update it.' link: We navigate
to the Update Virtual Hard Disk Parent page.

5) Enter the new location of the Basea.vhd file, In the top box,
enter 'C:\Bases\NewBaseFolder\Basea.vhd', 'Click Update Parent
Path':

At this point, we return to the 'Inspect Virtual Hard Disk' page. The
page reads: 'An error occurred while attempting to access the virtual
hard disk. The file "C:\Drives\toplevel.vhd" is not a valid virtual
hard disk.'

In addition, the event viewer now gives us our favorate old 'The
parent virtual hard disk appears to have been modified without using
the differencing virtual hard disk located at "C:\Drives
\toplevel.vhd". Modifying the parent virtual hard disk may result in
data corruption. It is strongly recommended that you lock the parent
virtual hard disk to prevent this in the future. If you recently
changed time zones on your computer, you can safely continue using
this virtual hard disk.' error.

However, if I inspect the middle layer drive, middledrive.vhd, it
shows the base, basea.vhd as being attached. Everything is sweetness
and light as far as the middle drive is concerned.

At this point, the only way, I've found, to recover that toplevel.vhd
is to open it up in VPC and discard changes.

Please, sir, tell me I'm doing something stupid.

Thanks and Cheers!
-Mezz

By the way, I've written code to update the headers as well. Never
did get the timestamp quite right, though. Seems like the
documentation is a single bit off at some points. Plus, I'd prefer to
use MS's published interfaces rather than going mucking about in
headers like I had to do for VPC. On the other hand, if I can't
figure this out, you might soon see a message from me requesting
assistance with finding the parent timestamp. *grin*

Thanks again,
-Mezz

On 4 Jun, 11:46, Richard Cardona <(email address - cut out)> wrote:

Show quoted text

> Mezz wrote:
> > I neglected to mention the version of VS I'm using:
> > Microsoft=AE Virtual Server 2005 R2 Service Pack 1 (SP1)
> > I believe this is the RC. I fetched it a few weeks back.
> > -Mezz
>
> In addition to updating VHD paths in Differencing disks, for the
> top-level VHD bound a to VM with Undo disks enabled, Virtual Server
> keeps track of the path to the parent of VUD in the .vmc configuration
> file - even though that data is redundantly stored in the VUD itself.
>
> If you ever need to move the parent of a VUD file you have to update the
> configuration information in the vmc for it to continue to work.

Re: Changing the locations of Base Drives in Virtual Server

Sent: 06/04/2007
From: Mezz <(email address - cut out)>
Message:

Thanks Richard,

Good to know I'm not crazy.
You know, using the touch -t is a pretty good idea. Its simple, and I
can't think of any reason why it won't work.

This is a .NET application, so before resetting the mid-layer vhd, I
can easily save the mod-timestamp and then reset it after setting the
base drive. This could be done in a recursive way for n-lvl deep
vhds.
I like that a lot more than hitting the binary header again. I've had
enough of that for one week, thank you.

The thing that bothered me most about this whole thing was that for
VPC, it was a warning, but for VS, it was registered as a warning that
manifested as an unrecoverable error. *grin* Well, saves on the
editing of error messages, I suppose.

Good call again, Richard.
If you're ever in Seattle, drop me a line. First beer is on me.
-Mezz

Re: Changing the locations of Base Drives in Virtual Server

Sent: 06/04/2007
From: Richard Cardona <(email address - cut out)>
Message:

Mezz wrote:

Mezz,
Thanks for your instructions and exact paths. I reproduced all of your
issues including the odd messages about the file being "in use" instead
of being moved and the Event View messages.

It turns out leaf or as you call them "top-level" VHDs are *highly*
dependent on the timestamp of their parents. That's what makes the file
"valid" or not. While updating Mid-level VHDs you must preserve the
timestamp (or alternatively patch the VHD's copy of the parent
timestamp). I was successful in breaking and repairing a mid-level VHD
with "touch".

These are steps I went through:
1. Made a new file, C:\Bases\BaseA.vhd
2. Made a mid-level VHD: C:\Middle\MIddle.vhd
3. Duplicated Middle.vhd to Copy of Middle.vhd (preserving the timestamps)
4. Created C:\Drives\TopLevel.vhd

Then without moving the base, I touched the modified timestamp of
MIddle.vhd. Afterwards, I inspected TopLevel.vhd and Virtual Server
told me the disk was "invalid," no if-ands-or-buts. I haven't even
modified it! Since Middle was "invalid" I moved BaseA.vhd to
C:\Bases\NewBase\BaseA.vhd and I repaired the parent link in Middle.Vhd
using Virtual Server with Inspect Disk.

Then using "Copy of Middle.vhd" for reference, I restored the
modificaiton timestamp to the repaired Middle.vhd using touch -t
<original date of modification> Middle.vhd

After I did this and inspected TopLevel.vhd, it was "valid" again with
the full chain represented all the way to new location of BaseA.vhd

So depending on your level of wanting to "hack" this, your choices
appear to be preserve file timestamps or patch top-level VHDs with their
parent's latest date of modification.

Richard

Show quoted text

> Thanks for the response, Richard.
> I've currently got a VM, same as the scenario I've described above.
> Its in perfect, happy working order, and I am able to start it. It
> currently has no vuds associated with it.
>
> Here's what I do.

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