L2 Primocache needed for .vhdx virtual drive hosted on another (already-cached) drive?

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gendrol
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L2 Primocache needed for .vhdx virtual drive hosted on another (already-cached) drive?

Post by gendrol »

I have an SSD providing L2 cache for my MS Storage Spaces array (drive F: formatted ReFS).

On this array (drive F:) I also have a .vhdx virtual drive mounted as drive G: and formatted NTFS. I require this for apps that don't support ReFS, such as OneDrive and Windows Image Backup.

My question is, if Primocache is already caching the Storage Spaces array on drive F:, does it also automatically cache drive G: which is actually a .vhdx file on F:? I understand Primocache works by inserting itself into the disk driver chain, so I'm not sure if Windows' mechanism to mount virtual drives will allow Primocache to cache the virtual drive automatically, or if perhaps that mechanism is below the level of Primocache in the chain.

If NOT, would I benefit from explicitly configuring Primocache to cache drive G: as well?

Thanks, any info would be appreciated!
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Re: L2 Primocache needed for .vhdx virtual drive hosted on another (already-cached) drive?

Post by Support »

Since .vhdx file is on a drive which has already been cached, it's not necessary to cache the virtual drive. However, you may still benefit from explicitly caching virtual drives. The reason is that it can reduce IOs between virtual drives and its VHDX file. The shortage is that data might be cached twice, wasting cache space.

Btw, we are still checking the compatibility with Refs. So you may just cache the drive G:.
gendrol
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Re: L2 Primocache needed for .vhdx virtual drive hosted on another (already-cached) drive?

Post by gendrol »

Thanks for your response.

It appears to work properly with ReFS. The cache task correctly lists the file system as "ReFS" and the L2Storage Read shows a positive cache hit rate of 13.3% and slowly increasing (I only started using Primocache a few days ago). But let me know if you discover anything else after you finish checking. Thanks!
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Re: L2 Primocache needed for .vhdx virtual drive hosted on another (already-cached) drive?

Post by Support »

Some users reported that sometimes Refs file system got corrupted with PrimoCache. So we are checking it.
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Re: L2 Primocache needed for .vhdx virtual drive hosted on another (already-cached) drive?

Post by gendrol »

I am using Primocache as a read-only L2 cache. So I should be safe from corruption even if it happens to others -- correct??

Thanks.
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Re: L2 Primocache needed for .vhdx virtual drive hosted on another (already-cached) drive?

Post by Support »

There was one report having the issue even without defer-write. It happened in version 3.x. Windows Storage Space creates 4Kn drives by default. We suspect that the Refs issue might be related to 4Kn drives. Now 4Kn drives have been fully supported since v4.2, so we are now running compatibility testing to check if the refs issue still exist or not. Thanks.
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