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Cache plays an integral part in RAID types that use parity or error checking and correcting (ECC). How much cache to put on a RAID card to get the best performance is a tricky bit of business: the natural reaction is to max it out. Below is a comparison of bechmarks using three sizes: 64, 128 and 256 MB PC133 SDRAM on a Promise FastTrak SX4000 with IBM DeskStar 75GXP 20 GB drives.
|
Adapter |
|
WinBench 99 |
IO Meter |
HD Tach |
|
ATTO |
|
||
|
|
|
|
High |
File |
|
Read |
Write |
1024k |
1024k |
|
Drive Configuration |
RAM |
Business |
End |
Server |
Database |
Average |
Average |
Write |
Read |
|
RAID 0 Two Disk |
|
|
|
|
|
|
|
|
|
|
IBM |
64 |
6640 |
26400 |
109.72 |
114.00 |
33227.6 |
28784.4 |
70393 |
82443 |
|
IBM |
128 |
5970 |
26200 |
109.58 |
113.35 |
33801.6 |
29936.2 |
70230 |
81640 |
|
IBM |
256 |
5480 |
25300 |
109.73 |
113.45 |
34177.7 |
29545.2 |
70393 |
81840 |
|
RAID 0 Three Disk |
|
|
|
|
|
|
|
|
|
|
IBM |
64 |
5700 |
27800 |
141.29 |
146.29 |
27634.1 |
30736.0 |
70558 |
97259 |
|
IBM |
128 |
5790 |
26500 |
140.90 |
146.45 |
27910.4 |
31639.2 |
69905 |
76959 |
|
IBM |
256 |
5730 |
26300 |
141.18 |
146.57 |
28157.3 |
31277.5 |
70393 |
95869 |
|
RAID 0 Four Disk |
|
|
|
|
|
|
|
|
|
|
IBM |
64 |
6070 |
26300 |
164.36 |
172.17 |
23622.4 |
30611.6 |
70393 |
94741 |
|
IBM |
128 |
6090 |
28200 |
165.50 |
173.35 |
23907.9 |
31081.9 |
69905 |
80082 |
|
IBM |
256 |
6120 |
28300 |
165.81 |
174.10 |
24215.0 |
31126.2 |
70558 |
97024 |
|
RAID 0+1 Four Disk |
|
|
|
|
|
|
|
|
|
|
IBM |
64 |
6240 |
25400 |
153.31 |
148.28 |
34004.4 |
29649.5 |
68015 |
81640 |
|
IBM |
128 |
5780 |
26500 |
153.40 |
148.28 |
32874.5 |
29579.0 |
67408 |
79324 |
|
IBM |
256 |
5730 |
26300 |
153.50 |
148.32 |
23973.8 |
31113.6 |
68169 |
80273 |
|
RAID 5 Three Disk |
|
|
|
|
|
|
|
|
|
|
IBM |
64 |
3930 |
16400 |
107.57 |
98.07 |
27045.6 |
21273.1 |
67710 |
65472 |
|
IBM |
128 |
4330 |
16500 |
107.39 |
98.33 |
27415.4 |
23638.2 |
64996 |
80659 |
|
IBM |
256 |
4320 |
15500 |
107.30 |
98.39 |
27540.5 |
23087.9 |
65312 |
81245 |
|
RAID 5 Four Disk |
|
|
|
|
|
|
|
|
|
|
IBM |
64 |
3850 |
17400 |
117.33 |
105.02 |
23548.6 |
22026.4 |
67710 |
70067 |
|
IBM |
128 |
4320 |
15900 |
117.90 |
105.37 |
23293.6 |
23374.7 |
67108 |
88512 |
|
IBM |
256 |
3760 |
16500 |
118.07 |
105.68 |
23548.8 |
23078.9 |
68634 |
91361 |
Well, after a lot of benchmarks it looks like maxing the cache paid off on four disk RAID arrays. For two disk arrays 64 MB is fine, and three disk arrays can go with any size.
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