How to Design storage for Citrix

In order to properly design the storage , we must first able to calculate the expected Input/Output Operations per Second (IOPS) requirements. The IOPS calculations must take the following into account:
Parameter Description Values
Disk Speed The speed that the disk spins has a direct impact on how fast the disk can read the correct sector. 15,000 RPM: 150 Random IOPS
10,000 RPM: 110 Random IOPS
5,400 RPM: 50 Random IOPS
Read/Write IOPS are broken down into reads and writes. Certain processes are read intensive while others require more writes. The ratio between reads and writes impacts of the overall IOPS. It has been shown that most desktop implementations result in the follow read/write ratios:
  • Reads: 20%
  • Writes: 80% |
RAID Level The RAID configuration impacts how many actual write IOPS are available due to the different types of redundancy in place. The write penalty reduces the overall IOPS for each disk spindle. RAID 0: No RAID Penalty
RAID 1: Penalty of 2
RAID 10: Penalty of 2
RAID 5 (4 disks): Penalty of 4

Desktop Lifecycle Each desktop goes through six phases, with each phase incurring different hits on the storage subsystem. Boot: 26 IOPS
Logon: 14 IOPS
Work:
  • Light: 4-8 IOPS
  • Normal: 8-12 IOPS
  • Power: 12-20 IOPS
  • Idle: 4 IOPS
  • Logoff: 12 IOPS
  • Offline: 0 IOPS

 Taking the six different parameters into account, we can calculate the IOPS requirements on a server-by-server basis and for the entire desktop virtualization architecture. The formula is as follows:

 Total Raw IOPS=Disk Speed IOPS*# Of Disks

 For example, if there are eight 146GB 15K SCSI3 drives in a RAID 10 configuration, the storage would have 720 functional IOPS.

 Functional IOPS=(((Total Raw IOPS×Write %))/(RAID Penalty))+(Total Raw IOPS×Read %)
With the functional IOPS calculated for the disk subsystem, the number of desktops that can be supported is based on the phase of the desktop lifecycle. Identifying how many desktops can be simultaneously logged in with this configuration is as follows:

 Total Raw IOPS=150×8=1200

 Functional IOPS=((1200× .8)/2)+(1200×.2)= 720

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