Host Cache Configuration and Virtual Flash

[marknashe]

Hi Community,

I'm trying to understand the difference between host cache configuration and virtual flash, and also what benefits do either of them have. I tried reading through to docs, but still don't get it. I have deployed 3 new servers, each have 2 SSD drives in them. I configured them as RAID1.  In the vSphere Client (software client), under configuration < Software , I see "Host Cache Configuration" and I see my local SSD's there. I have not checked the box for "Allocate space for host cache" yet. If I go into the Web Client and look under "Virtual Flash Resource Management", I don't see my SSD drives when I choose Add Capacity. I'm assuming maybe it's because my SSD's are in a RAID, but not 100% sure

I don't understand which one I should be using, or if I should use both?  It's for VDI environment

Thanks

Mark

[Matthew Larson]

Host Cache is essentially swapping to SSD.  More on that here‌ and here.  Put enough memory in the host, and you won't have any use for it.

Virtual Flash, called vFlash Read Cache is a host-based flash cache that can be broken up into chunks and assigned to virtual machines which will use said flash to cache frequently uses blocks rather than going to the SAN to get the data.  More on that here and here.  vFlash Read Cache requires an Enterprise Plus license.

In a VDI deployment - if you're using linked clones, you'd want to accelerate the replica VMs.  Unfortunately, you can not use a separate replica datastore if the datastore is to reside on local disk.

[marknashe]

Hi larsonm,

Thank you for reply. Yes, hosts have a ton of memory, so I doubt that will ever be an issue. I guess there's no point

We have not made a decision on VDI yet. Currently, just using a few full VMs, but considering a solution from Unidesk.

Do you know why I don't see the SSD for vFRC? Is it because the disks are raid?

I'll have a look at the links you provided.

[Matthew Larson]

Probably the RAID1 configuration.  Here are some items to review.

Also, vFRC isn't going to like if there's a file system (like VMFS) already on the drive.

[vAMenezes]

If you want to use it as vFlash, unmount and delete the datastore created on the SSD drive. Then you should see it on the vFlash Resource allocation page.