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#347561 - 23/09/2011 17:48 Would Readyboost help?
Phoenix42
veteran

Registered: 21/03/2002
Posts: 1392
Loc: MA but Irish born
For a conference next month I have the desire to run four VMs with a total memory allocation of 7GB, on my Win7 corporate laptop with 6GB of RAM. The run although slowly, might be better described as not snappy. One of the VMs is a SAN simulator, which is adding a chunk of IO to the disk, so off loading the RAM over commit to SD/USB would be an attractive option.

More RAM and SSD would be idea, but not something I can justify for one conference...

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#347562 - 23/09/2011 18:48 Re: Would Readyboost help? [Re: Phoenix42]
drakino
carpal tunnel

Registered: 08/06/1999
Posts: 7868
Loc: Seattle, WA
Readyboost likely won't help much in this particular situation. It's a caching mechanism of sorts, where Windows watches the I/O operations on the disk. Over time if it identifies access patterns better suited off a flash storage, it will migrate a copy there. Things like the windows boot process are accelerated, due to the flash drive allowing quicker random reads compared to a spinning disk.

As far as Windows is concerned, I/O access to your VM hard disk images is pretty random, and likely difficult to cache. It has no visibility into the files inside the virtual hard disks, so it can't tell the difference between the VM reading a specify file, or reading the file allocation table. If the VM hard disks are one solid file, it may never cache it, due to size. If it is set up as a sparse VM disk, then some pieces may make it into the cache if the chunks are small enough.

I will say it shouldn't hurt peformance either. If you already have a usable flash drive, give it a shot and see if it provides a noticeable benefit.
_________________________
Tom

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#347572 - 24/09/2011 05:36 Re: Would Readyboost help? [Re: Phoenix42]
Roger
carpal tunnel

Registered: 18/01/2000
Posts: 5620
Loc: London, UK
Originally Posted By: Phoenix42
so off loading the RAM over commit to SD/USB would be an attractive option.


ReadyBoost won't help much with RAM overcommit (paging). AFAIK, it only caches file read access, because Windows still has to be prepared for the device to be removed unexpectedly. As you can imagine, putting the pagefile on there would be a really bad idea.

Can you tweak the memory usage of the VMs down a bit? If you could shave 0.5Gb off two of them, you'd be back in-budget. Also, as far as the SAN simulator goes, you might get better performance if that I/O was backed by a physical disk or partition, rather than a VHD/VMDK file.
_________________________
-- roger

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#347584 - 25/09/2011 15:14 Re: Would Readyboost help? [Re: Roger]
Phoenix42
veteran

Registered: 21/03/2002
Posts: 1392
Loc: MA but Irish born
Just noticed that Workstation is reserving RAM for the host OS, which is a good idea, so my RAM budget is more like 4gb, so several of the VMs will need to go on a diet.
Unfortunately the SAN simulator isn't alterable, I believe it was originally created as a firmware testbed, rather than as a demo or educational tool, so performance wasn't a concern.

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