Designing Storage for Exchange 2003

Exchange Storage Design

The point of proper storage design is to ensure that each users gets enough IOPS. Consider the IOPS that the storage can provide:
* RAID 10 ( 2R 1W) RAID 5 (4R 1W)
* 15K rpm disks - 180 IO/second Before Controller
-Maximum Throughput = 180 X 80% (buffer) X .75 (RAID Factor) = 108 IO/second
-RAID 10 Factor = (R + W)/(R + 2W)
-RAID 5 Factor = (R + W)/(R + 4W)
* 10 Disks at RAID 10 - 1080 IO/second (Max IO/second that the disk will give you)
Using the example above, 1000 users would be able to receive 1.08 IOPS each.

JetStress can also be used to verify that 10 (15K RPM) disks at RAID 10 successfully sustain 1080 IOPS. Increasing the threadcount of JetStress will determine the most IOPS that those 10 disks can give you. As the thread count is increased, it's expected that the IOPS will not go above 1080.

Also, don't forget to consider IOs per database (since databases will be on seperate disks). If you pace 500 users on one database and 1500 on another, you will not achieve the required IOPS/user.

How many disks are needed?
To work this backwards we would need to following information:
* Mailboxes per server 1000
* Users I/O profile - 1.5 * IOPS = 1000 * 1.5 = 1500
*Read ratio(4 / (2+1) = .8
*Write Ratio (1 - .8) = .2
*RAID PENALTY for RAID 10 - 2 - Each write requires 2 disk I/O

(IOPS X Read Ratio) + [RAID Penalty](IOPS X Write Ratio)
-------------------------------------------
Spindle Speed Behind Controller (180)

*Result = 1800 / 180 = 10

Teo
Links:
Exchange Team Blog - Disk Sizing
Exchange Team Blog - Disk IO
Petri - Exchange Sizing