Romex Software Forum

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I'm looking for a caching solution for a Windows Server 2008 R2 physical server which is running the MS iSCSI target. The iSCSI target servers up LUNs that are accessed by two VMware hosts (LUNs are formatted as VMFS volumes). PrimoCache would seem to be a good candidate, as presumably it can do block level caching of the VHD files that the MS iSCSI target creates.

Alternatively, I could deploy PrimoCache within individual VMs.

Can someone comment on which of those options would provide the best performance?

Welcome to the forums Alozzy,

Running PrimoCache on the physical servers would probably be easier since you would only need 1 license per server, rather than 1 per VM. Also PrimoCache uses online activation which would likely require a separate activation with every new VM created.

However if your VM software uses a block-level driver for disk access, it will bypass PrimoCache in which case running within VMs would be the only option.

Sorry for the delay InquiringMind, I was on holiday

You said:

if your VM software uses a block-level driver for disk access, it will bypass PrimoCache in which case running within VMs would be the only option

I'm a little unsure what you mean. The ESXi hypervisor is configured for a software iSCSI adapter and all IO to the Windows Storage server is via iSCSI. However, the MS iSCSI target creates VHD files which in turn are exposed by the MS iSCSI target as LUNs. The LUNs are then formatted as VMFS volumes, with the ESXi hypervisor hosts accessing the LUNs via iSCSI over a dedicated LAN.

I'm hoping that, if PrimoCache is installed on the W2K8 R2 Storage Server, then PrimoCache will do block level caching of the VHD files.

Have I misunderstood?

alozzy wrote:I'm a little unsure what you mean. The ESXi hypervisor is configured for a software iSCSI adapter and all IO to the Windows Storage server is via iSCSI...

That iSCSI adaptor would probably be using a driver and, if so, may bypass PrimoCache's caching when it accesses data. If so, it would mean that you would not see any benefits from running PrimoCache on the host OS, but should see a benefit from running it within individual VMs.

It should be easy enough to check whether that situation applies in your case, with a quick test (using the likes of CrystalDiskMark) on the iSCSI volume with and without PrimoCache enabled.

Ok, thanks! Off to the lab to do some testing!