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BP1018 Sizing and Best Practices for Citrix XenDesktop with Dell EqualLogic Storage 34
Peak IOPS during boot storm
10000 15000
Peak IOPS during steady state
4500 9000
Capacity buffer
15%
18%
Based on our test results, I/O characteristics observed for the task worker type of workload profile
during the lifecycle of a virtual desktop can be summarized as shown in Table 7.
Table 7 I/O characteristics during the lifecycle of a VM
Type of I/O
IOPS per desktop
Read/Write ratio
I/O Block size
Steady state
7 - 8
0.2% / 99.8%
Read: 1KB /
Write: 9KB
Login storm 11 - 13 3% / 97% Read: 23KB /
Write: 5KB
Boot storm
16 - 18
13% / 87%
Read: 32KB /
Write: 5KB
Note: This IOPS estimation is based on the workload simulated by using Login VSI “Light” workload.
The number of IOPS during login storm and steady state may vary depending on the actual virtual
desktop environment. It is recommended to run a pre-deployment test to determine the exact IOPS
requirement.
Boot storm was simulated by restarting all Windows 7 virtual desktops from VMware vCenter. The boot
storm IOPS number can be used as a guideline for determining boot storm I/O for Windows 7 VDI
environments only when the Windows 7 image is created and tuned as described in section 7.4.3.
6.3 Sizing Calculations
IOPS is not the only key criteria while designing the storage solution. Calculating the storage capacity
is also an important aspect of designing storage for VDI environments.
Storage capacity requirements for pooled desktops using a PVS primarily depend on the following
factors:
• Number of vDisks to be created and maintained
• vDisk mode to be used
• OS installed
• Additional applications to be installed
• Storage location of the write cache file and size
• The type of I/O activity for each virtual desktop
The following formula may be used for determining how many virtual desktops can be deployed.
NumVM = (ArrayCApacity – (15% * ArrayCapacity + vDiskSize * NumvDisk))/ (125% * (VMem +
WCacheSize))