On Jun 16, 2006, at 6:28 AM, Greg Stark wrote:
I never understood why disk caches on the order of megabytes are
exciting. Why
should disk manufacturers be any better about cache management than OS
authors?
In the case of RAID 5 this could actually work against you since
the RAID
controller can _only_ use its cache to find parity blocks when
writing.
Software raid can use all of the OS's disk cache to that end.
IIRC some of the Bizgres folks have found better performance with
software raid for just that reason. The big advantage HW raid has is
that you can do a battery-backed cache, something you'll never be
able to duplicate in a general-purpose computer (sure, you could
battery-back the DRAM if you really wanted to, but if the kernel
crashed you'd be completely screwed, which isn't the case with a
battery-backed RAID controller).
The quality of the RAID controller also makes a huge difference.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@xxxxxxxxxxxxx
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@xxxxxxxxxxxxx
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
