On Thu, 29 Aug 2002 23:04, Jason Lim wrote: > IBM hard disks... with the superior cache algorithms, provide the highest > RAID 5 performance under high load of any drives available now... even > those ones with big 8Mb cache (was that WD or Seagate? anyway...). In > single drive mode, they are just average.
Interesting, I wonder what they do? I hope it's not agressive write-back caching without the request/permission from the OS/RAID... Some years ago a person on an OS/2 mailing list did some extensive tests of comparing various caching options. He discovered that if you used a largish (16M which was huge by the standards of the time) cache in the drive controller then no matter what he did with OS caching (HPFS had some good caching algorithms, and HPFS386 for LAN Server Advanced allowed cache size limited only by RAM) he could not increase performance much over the hardware cache (which was rather dumb). He needed at least 1M of cache in the OS (so that meta-data didn't require access to the drive controller) but after that caching lost much of it's benefit. Also he discovered that conversely using a large OS cache removed much of the benefit from a larger hardware cache, so basically performance was limited by the size of the largest cache. It would be really interesting to see such tests repeated with more recent OSs and hardware. -- I do not get viruses because I do not use MS software. If you use Outlook then please do not put my email address in your address-book so that WHEN you get a virus it won't use my address in the >From field.
