romatlo
Enthusiast
Enthusiast

System Disposable Disk questions?

Hello,

I am trying to understand a few things about System Disposable Disk.  The disposable disk is to contain the page file and temp directory for Windows, correct?

My master Win7 VM has 1 GB of RAM and a 1 GB page file.  What is the recommendation in general for a page file or could it be disabled all together?

I thought that the page file was represented by the .vswp file in the VM directory of datastore.  What is the difference between the .vswp and disposable disk?

What other examples of data are stored and lost in a Disposable Disk file?

See datastore pic attached.

Thanks!

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3 Replies
Linjo
Leadership
Leadership

Yes, your understanding is correct.

You should size your disposable disk to "Seize of swapfile + tempfiles".

As in many cases this answer is "it depends" but I usually start with halv the allocated ram as swap, so in this case 512MB.

The VMware swapfile (vswp) has nothing todo with the Windows swapfile, but kind of serves the same purpouse.

Since you have the ability to overallocate memory to VM:s, the host needs a "last way out" in case it runs out of memory, regardless what happends inside the VM. That is when it uses the vswp-file and write memory to disk. This is something that should be monitored and avoided if possible.

I usually recommend to set a "reservation" for the VM:s, maybe 2-300MB of memory, that will mean that the memory is always reserved for that VM and the vswp-file will be 2-300MB smaller since this reservation is in place.

Its also a way of protecting you from yourself overallocating too much since it will not allow you to power on more VM:s then you have reservations for.

Hope this helps.

// Linjo

Best regards, Linjo Please follow me on twitter: @viewgeek If you find this information useful, please award points for "correct" or "helpful".
romatlo
Enthusiast
Enthusiast

Thanks Linjo!

Yes that is helpful.  Just a few more comments and questions to round it off.

Since there is a VM swap file .vswp, is it even necessary to have a page file in the Win7 VM?  Should I just disable it?

When you say that you would start with 512MB, were you referring to the disposable disk size when creating the pool?

When you say since it I am allowed to overcommit memory, you are referring to the fact that vSphere allows this?

Is the .vswp file required and therefore will create a 1GB file (in this case) for each linked clone VM?

Please pardon my inexperience Smiley Happy.  Just having a hard time understanding the difference between the Windows page file, disposable disk, and VM swap file.

Thanks again.

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mittim12
Immortal
Immortal

The VM swap file is for when a VMware host runs out of memory so its not going to replace your Windows Swap file.  

VMware will allow you to overcommit memory and it comes in quite handy at times.   Read this pdf for some detailed information, http://www.vmware.com/files/pdf/techpaper/vsp_41_perf_memory_mgmt.pdf.  

The VM swap fille is required and will place a 1GB file (or equal to assigned memory) for each linked clone.   The only way around this is to reserve the memory on a clone.  This will allow you to save the 1GB but will hinder any type of memory overcommitment you try.