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Same Drives = Same Performance?


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Same Drives = Same Performance?
  January 21, 2001 Author: Terry Baranski  


IOMeter results

IOMeter - File Server Access Pattern - Load = Linear
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 65.94 0.71 15.16 ms 0.60 % 109.90
Drive B 65.78 0.71 15.20 ms 0.57 % 115.40
Drive C 65.57 0.72 15.25 ms 0.66 % 99.35
Drive D 65.97 0.72 15.15 ms 0.63 % 104.71

IOMeter - File Server Access Pattern - Load = Very Light
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 68.42 0.75 58.46 ms 0.71 % 96.37
Drive B 68.65 0.74 58.26 ms 0.60 % 114.42
Drive C 68.07 0.75 58.75 ms 0.66 % 103.14
Drive D 68.15 0.73 58.69 ms 0.65 % 104.85

IOMeter - File Server Access Pattern - Load = Light
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 79.64 0.87 200.86 ms 0.79 % 100.81
Drive B 79.23 0.86 201.86 ms 0.73 % 108.53
Drive C 78.54 0.85 203.65 ms 0.80 % 98.17
Drive D 78.49 0.85 203.82 ms 0.73 % 107.52

IOMeter - File Server Access Pattern - Load = Moderate
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 89.25 0.96 716.68 ms 0.96 % 92.97
Drive B 89.00 0.98 718.76 ms 0.90 % 98.89
Drive C 88.08 0.95 726.25 ms 0.95 % 92.72
Drive D 88.29 0.95 724.60 ms 1.00 % 88.29

IOMeter - File Server Access Pattern - Load = Heavy
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 98.65 1.07 2591.71 ms 1.35 % 73.07
Drive B 98.09 1.06 2606.49 ms 1.31 % 74.88
Drive C 97.25 1.05 2626.84 ms 1.28 % 75.98
Drive D 97.43 1.06 2622.30 ms 1.35 % 72.17

IOMeter - Workstation Access Pattern - Load = Linear
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 77.36 0.60 12.92 ms 0.83 % 93.20
Drive B 76.73 0.60 13.03 ms 0.83 % 92.45
Drive C 76.48 0.60 13.07 ms 0.71 % 107.72
Drive D 76.37 0.60 13.09 ms 0.74 % 103.20

IOMeter - Workstation Access Pattern - Load = Very Light
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 79.84 0.62 50.10 ms 0.80 % 99.80
Drive B 79.19 0.62 50.50 ms 0.74 % 107.01
Drive C 78.50 0.61 50.95 ms 0.74 % 106.08
Drive D 78.52 0.61 50.94 ms 0.79 % 99.39

IOMeter - Workstation Access Pattern - Load = Light
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 91.75 0.72 174.34 ms 1.00 % 91.75
Drive B 91.44 0.71 174.96 ms 0.88 % 103.91
Drive C 89.78 0.70 178.19 ms 0.95 % 94.51
Drive D 90.26 0.71 177.22 ms 0.91 % 99.19

IOMeter - Workstation Access Pattern - Load = Moderate
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 102.58 0.80 623.55 ms 1.13 % 90.78
Drive B 101.51 0.79 630.15 ms 1.02 % 99.52
Drive C 100.63 0.79 635.77 ms 0.98 % 102.68
Drive D 100.95 0.79 633.68 ms 1.03 % 98.01

IOMeter - Workstation Access Pattern - Load = Heavy
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 111.90 0.87 2284.06 ms 1.54 % 72.66
Drive B 111.77 0.87 2286.81 ms 1.59 % 70.30
Drive C 110.31 0.86 2317.64 ms 1.56 % 70.71
Drive D 111.07 0.87 2301.64 ms 1.49 % 74.54

IOMeter - Database Access Pattern - Load = Linear
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 70.68 0.55 14.14 ms 0.74 % 95.51
Drive B 70.11 0.55 14.26 ms 0.66 % 106.23
Drive C 69.75 0.54 14.33 ms 0.70 % 99.64
Drive D 69.47 0.54 14.39 ms 0.68 % 102.16

IOMeter - Database Access Pattern - Load = Very Light
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 72.35 0.57 55.28 ms 0.75 % 96.47
Drive B 72.04 0.56 55.52 ms 0.73 % 98.68
Drive C 71.02 0.55 56.31 ms 0.66 % 107.61
Drive D 71.26 0.56 56.13 ms 0.69 % 103.28

IOMeter - Database Access Pattern - Load = Light
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 82.40 0.64 194.13 ms 0.85 % 96.94
Drive B 82.51 0.64 193.88 ms 0.78 % 105.78
Drive C 81.47 0.64 196.37 ms 0.79 % 103.13
Drive D 80.76 0.63 198.07 ms 0.85 % 95.01

IOMeter - Database Access Pattern - Load = Moderate
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 91.47 0.71 669.39 ms 0.99 % 92.39
Drive B 90.90 0.71 703.72 ms 0.97 % 93.71
Drive C 89.93 0.70 711.24 ms 0.91 % 98.82
Drive D 89.99 0.70 710.95 ms 1.01 % 89.10

IOMeter - Database Access Pattern - Load = Heavy
IOMeter Tests IO/sec MB/sec Response Time CPU Util. IO/CPU%
Drive A 99.44 0.78 2570.32 ms 1.40 % 71.03
Drive B 98.70 0.77 2588.35 ms 1.38 % 71.52
Drive C 98.05 0.77 2606.30 ms 1.35 % 72.63
Drive D 97.78 0.76 2612.42 ms 1.38 % 70.86

The first thing that stands out about the above IOMeter scores is that all drives score very, very closely to one another in each of the 15 tests. In fact, the average difference between the highest and lowest score for any given test is only 1.33 IO/sec. But is 1.33 IO/sec within IOMeter's margin of error, or is it an indication that the drives are performing differently from one another? Attempting to answer this question, we ran IOMeter on one of the DM 80's four times. Once these four runs were completed, we calculated the average difference between the highest and lowest score for each test. In this case, the result was 0.63 IO/sec. This indicates that the differences in scores we're seeing with these four drives are not entirely a product of the benchmark itself.

With this in mind, it's interesting to take a look at which drives are performing better, and which ones are performing worse. As some may know, SR's IOMeter tests consist of a total of 15 runs: 3 access patterns, with 5 variations of "outstanding IOs per second" in each one. The table below shows how many times each drive finished a test with a given rank (1st place, 2nd place, etc):

IOMeter Rank Analysis
IOMeter RankDrive ADrive BDrive CDrive D
First Place 12 2 0 1
Second Place 3 12 0 0
Third Place 0 1 5 9
Fourth Place 0 0 10 5

This table reveals some very interesting figures. For example, drive A presents the best score in 12 out of the 15 IOMeter tests. In the other 3 tests, turns in the second-best score. Drive B gets the silver metal by managing the second-place in 12 out of the 15 tests. Drives C and D, however, both finished in either 3rd or 4th place in all but 1 test.

So what do these figures mean, if anything? Due to the consistency between various IOMeter tests, it is our belief that they indicate very, very slight differences in performance between the four drives. It's impossible to pinpoint the cause of these small differences, but it seems likely that slight differences in average seek time are responsible. How much of a difference is required to cause these small variations in IOMeter scores? We saw above that WinBench reports small differences in access time, yet we've explained why we're a bit wary of placing our complete trust in those results. Wouldn't it be nice if we could test access time with IOMeter as well?

Although the IOMeter scores above include an "average IO response time" category, seek time cannot be accurately determined from this metric since all of SR's IOMeter access patterns include a certain percentage of writes and/or sequential IO's. Therefore, we ran the following IOMeter access pattern on each of the four drives:

IOMeter Access Time Specification
Transfer Size Request 512 bytes
% Reads 100%
% Random 100%

The test was run with just one outstanding IO to eliminate the effects of IO reordering. (When commands are reordered for optimal head movement, average seek time cannot be measured since average seek distance tends to decrease as the number of outstanding commands increases.) Like all of SR's IOMeter tests, this pattern was run for 10 minutes with a 30 second ramp-up time. The test was run on each drive twice. The average results:

IOMeter Access Time Test
IOMeter TestsDrive ADrive BDrive CDrive D
Total I/Os per Second 64.97 64.79 64.25 64.53
Total MBs per Second 0.0317 0.0316 0.0314 0.0315
Average I/O Response Time (ms) 15.38 15.43 15.55 15.49
Maximum I/O Response Time (ms) 31.88 46.58 47.49 46.06
% CPU Utilization (total) 0.61 0.58 0.54 0.56
CPU Effectiveness (IO/%CPU) 105.61 110.95 117.37 113.31

The important field is "Average IO Response Time", which represents the drive's average access time in this particular test. The above results are consistent with the previous IOMeter scores, as well as with WinBench access time scores. Note that the order in which the drives finished (from best to worst) in this test is A-B-D-C- exactly the same order the drives finished the WinBench access time test. Also, looking back at the IOMeter rank table, one again sees the same A-B-D-C pattern.

It is, however, interesting to note that the Average IO Response Times shown above - despite showing the same A-B-D-C pattern as the WinBench access time scores -- are consistently higher by about 0.30ms on average. The cause? There are two known differences between these tests: 1) IOMeter's test runs for a much longer period of time, and 2) IOMeter tests are run on unformatted drives, while all WinBench tests must be run on a drive that is formatted. Excluding these differences, the tests should be the same - they both presumably read random sectors, and as a result test access time in the same way. We fail to see how the 2nd difference would affect the scores; however, we mentioned earlier that we have more faith in a test that takes longer to run, so it's very possible that reason number 1 is at least partially responsible for the differences.

 Conclusion...


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