Re: ATA Drive Selection (Reliability)...
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.
--
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