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Disk write errors

Source: microsoft.public.virtualpc
Sent: 02/09/2008
From: clucas009
Message:

Here is the setup,

Host Machine:
Dell dual core Xeon 2Ghz x2 running Windows 2003 Server
2x 320GB hard drives mirrored - 3 Partitions (1 - OS, 2 - Virtual PCs, 3 -
Data)
4GB ram

Virtual PC:
Windows XP pro which are connected to by a thin client box (PCExpansion box)

I am looking at installing an application that uses SQL express. The
database will be stored on the data partition. The thin clients will be
connected to the virtual machine and accessing the database. It was
mentioned to me that there may be some disk errors due to the database and
the VM running on the same physical drives even though they are on different
partitions. I have not heard or been able to find any information supporting
this but wanted to see if anyone else has heard of disk errors when using VM.

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Related Messages

Re: Disk write errors

Sent: 02/09/2008
From: Bo Berglund <(email address - cut out)>
Message:

On Sat, 9 Feb 2008 05:35:00 -0800, clucas009
<(email address - cut out)> wrote:

So your *host* has 3 partitions. So far fine....
You do not mention in *which* PC you are installing the application
that uses SQLExpress, but presumably this is on the *host*, right?
Otherwise your statemant about putting the database on the 3rd
partition does not make any sense at all.

In this scenario the guest OS will have its virtual disk file stored
on the 2nd partition and SQLExpress *on the host* will have its
database stored on partition 3.

What will now happen is that the head of your single physical disk
drive will have to jump back and forth across the disk surface
constantly because when it accesses host OS data it needs partition 1,
when the guest OS wants to access its disk it jumps to partition 2 and
finally when the host SQLExpress accesses the database it jumps to
partition 3. This means *a lot* of disk head moves and slows the
operations down considerably. Disk errors should not be caused by this
but performance is surely degraded.

You should consider at least moving the virtual machine hard disk file
to a separate host drive so its head can stay stationary.
Putting the database on a separate physical drive also helps but that
depends on the workload of the database server, at light loads it
might not be significant.
If you want to really optimize the speed of the database server you
should use one physical disk for each of:
- The host operating system
- The Database file
- The database log file
- The virtual machine virtual disk file

Bo Berglund

Show quoted text

>Here is the setup,
>
>Host Machine:
>Dell dual core Xeon 2Ghz x2 running Windows 2003 Server
>2x 320GB hard drives mirrored - 3 Partitions (1 - OS, 2 - Virtual PCs, 3 -
>Data)
>4GB ram
>
>Virtual PC:
>Windows XP pro which are connected to by a thin client box (PCExpansion box)
>
> I am looking at installing an application that uses SQL express. The
>database will be stored on the data partition. The thin clients will be
>connected to the virtual machine and accessing the database. It was
>mentioned to me that there may be some disk errors due to the database and
>the VM running on the same physical drives even though they are on different
>partitions. I have not heard or been able to find any information supporting
>this but wanted to see if anyone else has heard of disk errors when using VM.

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