possible to benefit from PrimoCache for both host and VM?

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support
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Re: possible to benefit from PrimoCache for both host and VM?

Post by support » Sun Mar 25, 2018 3:10 pm

As Axel Mertes said, PrimoCache on Windows Host OS can improve any VM by using SSD caching.
If you have enough RAM for VM, you may also try L1 writing cache (Defer-Write on) inside VM, this will help VM writing performance a lot and it is much faster than doing L1 writing cache on Host OS.
quirken wrote:Optane would require a new computer they require a newer processor
If you use Optane SSD as a cache device with PrimoCache, this is not required.
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Widdershins
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Re: possible to benefit from PrimoCache for both host and VM?

Post by Widdershins » Wed May 15, 2019 1:50 am

It seems this may not be holding true at the moment for VMs with a secondary virtual hard drive attached to my VirtualBox x64 setup 5.2.28 r130011. Primo caches host block reads fine on a Win10 x64 17763.475 host (cache task 1)

It also caches guest (also Win10 x64 17763.475) block reads fine of the VMs boot VDI that resides on host volume V. (cache task 2)

The VM has a secondary VDI attached to it that resides on host volume S and inside the guest is labeled as "Secondary Storage". (cache task 3)

When I boot up the VM I see the following blocks read from the S volume

Image

Yet, when I actually read/write several gigs to the guest "secondary storage" volume, none of the block reads are picked up by PrimoCache. If relevant, the difference between the boot VDI and the Secondary Storage VDI is the boot VDI was created as "dynamically allocated" whereas the Secondary Storage VDI was created as "fixed size" because it's a spinning disk and I didn't want the VDI to be fragmented.

I tested it with the VM sata controller set to "use host IO cache" and also with that disabled yet the behavior is unchanged.

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Re: possible to benefit from PrimoCache for both host and VM?

Post by support » Thu May 16, 2019 4:56 pm

We tested with configurations as yours, but we don't see the problem. PrimoCache works whether you use "dynamically allocated" or "fixed size" virtual disks. Could you confirm that the guest secondary storage is on the volume S which is cached? You may also check if reading on the secondary storage was not cached by Windows cache.
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Jaga
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Re: possible to benefit from PrimoCache for both host and VM?

Post by Jaga » Thu May 16, 2019 6:09 pm

support wrote:
Thu May 16, 2019 4:56 pm
We tested with configurations as yours, but we don't see the problem. PrimoCache works whether you use "dynamically allocated" or "fixed size" virtual disks.
I can confirm this as well - using 2 VMs each with dynamically allocated volumes, and both are caching reads/writes through the host's Primocache task. Neither has a secondary volume attached, though I don't see how that would affect IO significantly. Might be just what Support suggests - a configuration problem.

Widdershins
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Re: possible to benefit from PrimoCache for both host and VM?

Post by Widdershins » Fri May 17, 2019 4:58 am

Further down the rabbit hole...Check this out this behavior of the caching of the secondary volume to V cache instead of the intended S cache.

https://www.youtube.com/embed/Fufp-ZBQyEk?vq=hd1080


@support I've yet to observe corruption, yet as you'd expect it's desirable that S be it's own cache for a couple reasons. The REFS volume is 64k and the ignored S cache is 64k. It's undesirable S be herded into the 4k V cache because it's the incorrect block size and it makes it impossible for me to uniquely monitor the S cache and reset it without affecting the V cache contents.

Is this behavior the same under Windows 10 Hyper-V ??

Oh and I updated to VirtualBox 5.2.30 that rolled yesterday just in case. Same behavior. I'm not using 6.0.8 yet because a Debian guest loses a convenient feature, yet I'd reconsider if PrimoCache functions as desired on 6.x I appreciate your help.

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Re: possible to benefit from PrimoCache for both host and VM?

Post by support » Mon May 20, 2019 6:22 pm

@Widdershins, we watched the video. Could you make sure that the S drive in your VM is located in the virtual disk "Sandbox Storage.vdi"? Or could you show us the Window Disk Management in your VM?
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Widdershins
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Re: possible to benefit from PrimoCache for both host and VM?

Post by Widdershins » Mon May 20, 2019 8:54 pm

Nothing is hardlinked/junctioned from S: back to the boot volume C (Boot VDI on volume V).

Image

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Re: possible to benefit from PrimoCache for both host and VM?

Post by support » Wed May 29, 2019 11:28 am

Could you check a different file on S: drive? This problem might be related to Windows Data Deduplication technique.
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