Blast from the past: originally published in 2003.

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 benchmarks using three sizes: 64, 128 and 256 MB PC133 SDRAM on a [intlink id=”214″ type=”post”]Promise FastTrak SX4000[/intlink] 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.