vSphere 6 Setting up vFlash Read Cache

This example is being performed on a Dell R630 with the Perc RAID controller running ESXi 6.  I didn’t do anything special with the Flash disk in the RAID controller, I simply created a RAID 0 volume group with the single drive.

A lot of the inspiration for this fix is from this Yellow Bricks post.

Once the Host has ESXi installed, network configured, booted up, added to vCenter (and all the extra gubbins done), you will first need to mark the disk as a Flash disk …… ESXi won’t pick this up automatically.

vsphere_6_vflash_read_cache_1Manage > Storage > Storage Devices > Highlight disk and click the F button to mark as Flash.

vsphere_6_vflash_read_cache_2Now right-click the ESXi host > Storage > Add Virtual Flash Resource Capacity.

At this point I ran into a problem.  As far as I can see you should simply be able to add the Flash drive as Virtual Flash Resource Capacity, however, by default it was greyed out and isn’t selectable……

vsphere_6_vflash_read_cache_3…… and it only becomes selectable if you click the “Enable remote flash selection” tickbox.

vsphere_6_vflash_read_cache_4When you click OK, vCenter tells you it has completed, however, there are no Flash Datastores available for use and I was getting the following error under the ESXi Host > Monitor > Events:-

Configuration on disk /vmfs/devices/disks/naa.614187704de041001e622fd406f5f19e failed. Reason : A specified parameter was not correct: naa.614187704de041001e622fd406f5f19e

This fix for this is to tag the disk from esxcli, so next SSH into your Host and run

You will see that ESXi has detected this disk as a remote SAS SSD.

vsphere_6_vflash_read_cache_5If you try and add the disk as local (as per the comments in the Yellow Bricks post) you will get the following error:-

Error adding SATP user rule: Duplicate user rule found for SATP VMW_SATP_LOCAL matching device naa.614187704de041001e622fd406f5f19e PSP and PSP Options

vsphere_6_vflash_read_cache_6So to resolve this you will need to remove the rules, readd them correctly, run reclaim and then (back in the Web Client) retag as flash.

Once this is done you should be able to add flash correctly.


One Reply to “vSphere 6 Setting up vFlash Read Cache”

  1. Just wanted to thank you for such an excellent write-up. We just ran through this with a customer.

    Turns out he had previously created a VMFS datastore on this SSD which is how the original rule got created.

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