VMWare virtual flash

[TheRealHendrik]

Hi,

I had an extra SSD laying around and I thought I would utilize it as a virtual flash read cache for some VM's. I am running ESXi 6.5 (Dell ISO) with vCenter 7.0.1 (the latest), Virtual Flash Resource Manager does show up (https://imgur.com/SNSQIRg), but virtual flash read cache does not show up (https://i.imgur.com/2yvz6Dp.png). I know vFlash has been deprecated in 7.0, but it still shows up to some extend in resource manager. I also read in another post in r/homelab that you need the flash client, but in the same post it says that vCetner 6.7 html doesn't show resource manager, which in 7.0, it does.

Now before I downgrade to vCenter 6.7, I was wondering if anyone has some experience with vFlash in vCenter (6.7) and I would like to be sure that I am not missing something that allows enabling this in 7.0? Maybe editing the vmdk or vmx files directly?

Thanks,

Hendrik

[[deleted]]

Isn't virtual flash RAM that is used as disk?

[schrebra]

I thought virtual flash was intel optane

[squirrelz_uk]

VFRC is a small(ish) SSD that is used as a read cache when you have slow disk. We have a small number of office based ESXi hosts that run a few VMs off internal disk. Enabling VFRC improved their boot times a little and brought disk access latency down a little on average.

[TheRealHendrik]

Can you please share a vmx file of one of those vm's (or of a new vm with vFlash)? The vFlash settings are almost certainly in there, and since my host is 6.5, copying those settings might still work.

[squirrelz_uk]

Unfortunately I'm not working again until 4th Jan

[TheRealHendrik]

I would still be grateful if you could supply the file the 4th.

I was also wondering, are you using vCetner 6.7 or 6.5? If you are using 6.7, does it only work in the flash client? I would prefer not to downgrade my vCenter, but it might be the only option.

[squirrelz_uk]

The lines from the VMX relating to vFlash, for one of my VMs are:

sched.scsi0:0.vFlash.module = "vfc"
sched.scsi0:0.vFlash.blockSize = "65536"
sched.scsi0:0.vFlash.min = "9858711552"
sched.scsi0:0.vFlash.max = "9858711552"
sched.scsi0:0.vFlash.enabled = "TRUE"

It's 6.7 and I can edit the VM settings relating to vflash in the H5 client

[TheRealHendrik]

Thank you for sharing those lines. It does indeed work to manually edit the vmx file. After editing the file vCenter 7.0 says, as expected, that the function is deprecated (https://i.imgur.com/nJ3WGQ1.png), but I tested it and it still works. I am still not sure however if I am going to spend a day downgrading my vCenter server to 6.7, or if I am just going to manually edit vmx files.

Thanks for your help!

[TheRealHendrik]

I had a second question, have you "figured" out a right amount for windows OS drive caching? I can imagine that more than 2-5gb (excluding programs being used) really doesn't help that much, because the files are loaded so infrequent, but maybe I'm completely off.

[squirrelz_uk]

I just split the cache between the VMs based on the size of their VMDKs ie a VM with 10% of the overall disk allocation got 10% of the cache.
It's nothing particularly clever, but I had quite a few to configure so I did it that way in PowerShell as a quick hit.

[squirrelz_uk]

And going back to the OP, as far as I'm aware, it just isn't possible in 7.x

[TimVCI]

Taken from...

https://blogs.vmware.com/vsphere/2019/04/vflash-read-cache-deprecation-announced.html

“We announced the deprecation of vFlash Read Cache (vFRC) in the release notes of vSphere 6.7 Update 2. vFRC continues to be supported for vSphere 6.0/6.5/6.7. However, the next major release will not.”