Windows Host, Windows Client Write Behind Buffer

[Cool Javelin]

Hello,

Is there a way to turn off WinXP (sp3) write behind buffer in a VirtualBox Client?

Since there is already a write behind buffer in the host (when VB wants to write to the host drive) I think it is not really necessary to have a second write behind buffer in the client.

Any thoughts on how this might impact client performance?

Thanks, Mark.

[loukingjr]

Hello,

Is there a way to turn off WinXP (sp3) write behind buffer in a VirtualBox Client?

Since there is already a write behind buffer in the host (when VB wants to write to the host drive) I think it is not really necessary to have a second write behind buffer in the client.

Any thoughts on how this might impact client performance?

Thanks, Mark.

VB doesn't write to the host drive, it writes to a .vdi file on the host drive.

[mpack]

I'm not entirely sure what a "write behind buffer" is. When I try to think what it means, it always self simplifies to "buffer".

Anyway, you can turn host I/O caching off if you like, in the VM settings. You can test for yourself whether any impact on performance is acceptable to you.

[loukingjr]

Anyway, you can turn host I/O caching off if you like, in the VM settings. You can test for yourself whether any impact on performance is acceptable to you.

As it turns out it's a good idea to turn off host I/O caching on OSX 10.9 Hosts, perhaps 10.8 hosts as well. Because of the Mac's file management, having it enabled acts like a memory leak. It's not, but it behaves like one. I posted something about it in the Mac Hosts section. I'm not sure if it does the same thing on other hosts.

[Cool Javelin]

The "Write behind buffer" I am thinking about may be called "delayed write" in some systems.

When a program writes to the disk, Windows cache's it for performance, then writes to the slow disk later. In the olden days (Circa Win3.1) M-Soft had a program called "Smartdrive" to do that.

Since there are really 2 operating systems (one called the host, the other called a client,) I am sure there are 2 caches.

Having 2 caches won't improve performance any more then one, but it will use more memory then needed, as well as reduce reliability. Also, it will take longer for the client to shut down if it has to flush the cache beforehand. (Although it won't be too bad as it will be flushing to another cache in the host.)

I understand VB actually writes to a VDI file, that is what I meant when I said "writes to the host drive."

I see a couple ideas about turning off "Host caching." for OSX, I am running WinXP as a host. Can someone tell me where to look to try this?

I assume you are talking about between Virtual Box and the host OS, not inside the VB client. Can this be done on a program by program basis? For example, can I turn off host caching for Virtual Box, and not for my other programs like Excel (running on the host.)?

Mark.

[mpack]

Look in the Storage settings for the host cache option.