Interesting VDI facts

Posted on by storagehacker

Most of the Virtual Desktop Infrastructure (VDI) sizing and performance papers found from the virtualization companies and storage companies state that for sizing purposes a range of 5-20 I/O per seconds (IOPs) should be used.  Using this range as ESG Labs did in their Lab report on HP LeftHand P4000 SAN – Optimizing Virtual Desktop Infrastructure with Citrix XenDesktop with 5 IOPs being the Optimistic number and 20 IOPs being the Conservative number administrators can use the storage vendors stated IOPs to determine the number of VDI users per storage array.  The lab report provided the following table:

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The Xiotech Emprise 5000 with 7.8TB of useable RAID5 storage and linear expansion using the above IOP figures provide the following level of VDI Users:

Number of ISEs IOPS Virtual Desktops Conservative Virtual Desktops
Optimistic		 Response Time
(ms)
2 7,000 350 1,400 27
4 14,000 700 2,800 27
10 35,000 1,750 7,000 27
15 52,500 2,625 10,500 27
20 70,000 3,500 14,000 27
However, these numbers does not take into account the fact the VMs require a certain amount of disk space for the installed Guest OS and applications that the VDI users need.  Using VMs configured with Microsoft Windows XP SP3 with a 20GB disk the number of VMs that a Xiotech ISE with 7.8TB of RAID5 usable space could service would actually look more like this:
Number of ISEs Number of VMs
with a 20GB disk		 Number of VMs
with a 30GB disk
2 696 464
4 1,392 928
10 3,480 2,320
15 5,220 3,480
20 6,960 4,640

Each ISE is only 3U and is able to provide a very high density of VDI users with excellent performance and reliability.  Given most hypervisor vendors recommend 32-64 VDI VMs per physical host this configuration allows for 40U of rackspace to provide 1392 end users virtual desktops (using twenty-four 1U servers, four 1U FC Switches, and four ISEs).  The gains would be all the redundancy of the hypervisors high availability features, resource management, datacenter power redundancy (UPS and/or Generator) and the ability to enhance security by having all corporate data actually in the datacenter, opposed to user desktops and laptops.

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