Average ratio of VMs per LUN

[Mohamed-Roushdy]

Hello,

We are using VMware with NETAPP AFF8080, my question is, what's the recommended VM count per LUN that we should not exceed, especially when it comes to VDI VMs?

Thank you,

[GidonMarcus]

I think there's two variables to consider.

the first is any serial operation that done on a LUN level. in modern OS (like Cdot) the serial operations will be to much smaller chunks, but in ONTAP pre 8.1 and in other vendors, some serial operations are bound to a LUN. which could create a bottleneck.

The other variable is the SCSI queue depth. in VMWare there's a 32 deep queue per path - per LUN. if you see the queue getting bigger and bigger, you should either add path's or split the workload to multiple LUNs (assuming there's no underling bottleneck that causing the queue growth)

there is also a theory that you better move workload with sequential workload away from random ones, as it will perform better for the sequential and prevent the random IOs on the same LUN to wait behind for the sequential.

Gidi

[Mohamed-Roushdy]

Thanks for the info, but, is there a max recommended limit for VDI? like 30 (for instance) per datastore? VDIs  are just VDis not running any sequential workloads.

[GidonMarcus]

VDI can be sequential and impacting in a boot storm or Anti Virus scan for example. i don't know about other limitation. worth to maybe create a boot storm of your own and see how is it impacting the queue length, latency and other parameters.