While I was at TechEd, I had a great time talking with our customers and hearing about their experiences as Exchange administrators. One of the areas that have come up in discussion a lot has to ...
Updated Jul 01, 2019
Version 2.0
Blog Post
To measure your R:W ratio, look at the ratio of LogicalDiskDisk Reads/sec to LogicalDiskDisk Writes/sec for the database drives. (You can look at the same counters in PhysicalDisk if you don't have the LogicalDisk counters enabled).
Note that for corporate servers with a large number of users (I am defining large here as 500 users or more), the R:W ratios are usually 3:1 or 2:1. However, servers that have fewer than 500 users will have lower R:W ratios (approaching 0:1 as the number of users decreases and as the amount of data in the database decreases). This is because for servers with few users, much of the user’s data will be in the database cache (in memory), so some of the read actions will be satisfied by data in memory. This reduces the number of read operations. Of course, all of the write operations will still have to be written to disk. Thus, the net effect of having a smaller number of users on the server is that the ratio of R:W goes down.
Below are the values for R:W ratio of 0:1.
R:W ratio Disk speed: 130 IOs per second 180 IOs per second
0:1 104 IOPS 144 IOPS
Table 2. Estimated maximum disk throughput for Raid 0+1 (or Raid 10):
R:W ratio Disk speed: 130 IOs per second 180 IOs per second
0:1 52 IOPS 72 IOPS
Table 3: Estimated maximum disk throughput for Raid 5:
R:W ratio Disk speed: 130 IOs per second 180 IOs per second
0:1 26 IOPS 36 IOPS
Note that for corporate servers with a large number of users (I am defining large here as 500 users or more), the R:W ratios are usually 3:1 or 2:1. However, servers that have fewer than 500 users will have lower R:W ratios (approaching 0:1 as the number of users decreases and as the amount of data in the database decreases). This is because for servers with few users, much of the user’s data will be in the database cache (in memory), so some of the read actions will be satisfied by data in memory. This reduces the number of read operations. Of course, all of the write operations will still have to be written to disk. Thus, the net effect of having a smaller number of users on the server is that the ratio of R:W goes down.
Below are the values for R:W ratio of 0:1.
R:W ratio Disk speed: 130 IOs per second 180 IOs per second
0:1 104 IOPS 144 IOPS
Table 2. Estimated maximum disk throughput for Raid 0+1 (or Raid 10):
R:W ratio Disk speed: 130 IOs per second 180 IOs per second
0:1 52 IOPS 72 IOPS
Table 3: Estimated maximum disk throughput for Raid 5:
R:W ratio Disk speed: 130 IOs per second 180 IOs per second
0:1 26 IOPS 36 IOPS