RAID Cache Size

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 Promise FastTrak SX4000 with IBM DeskStar 75GXP 20 GB drives.

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.

AdapterWinBench 99IO MeterHD TachATTO
HighFileReadWrite1024k1024k
Drive ConfigurationRAMBusinessEndServerDatabaseAverageAverageWriteRead
RAID 0 Two Disk
IBM64664026400109.72114.0033227.628784.47039382443
IBM128597026200109.58113.3533801.629936.27023081640
IBM256548025300109.73113.4534177.729545.27039381840
RAID 0 Three Disk
IBM64570027800141.29146.2927634.130736.07055897259
IBM128579026500140.90146.4527910.431639.26990576959
IBM256573026300141.18146.5728157.331277.57039395869
RAID 0 Four Disk
IBM64607026300164.36172.1723622.430611.67039394741
IBM128609028200165.50173.3523907.931081.96990580082
IBM256612028300165.81174.1024215.031126.27055897024
RAID 0+1 Four Disk
IBM64624025400153.31148.2834004.429649.56801581640
IBM128578026500153.40148.2832874.529579.06740879324
IBM256573026300153.50148.3223973.831113.66816980273
RAID 5 Three Disk
IBM64393016400107.5798.0727045.621273.16771065472
IBM128433016500107.3998.3327415.423638.26499680659
IBM256432015500107.3098.3927540.523087.96531281245
RAID 5 Four Disk
IBM64385017400117.33105.0223548.622026.46771070067
IBM128432015900117.90105.3723293.623374.76710888512
IBM256376016500118.07105.6823548.823078.96863491361

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.