"Ross J. Reedstrom" wrote:
>
> On Wed, Dec 15, 1999 at 11:27:36AM -0400, The Hermit Hacker wrote:
> > On Wed, 15 Dec 1999, Jeff Hoffmann wrote:
> >
> > Most of my RAID tests are on Solaris+Disksuite...with good drives
> > in the machine, my writes are something like 18MB/s to the drive, stripe'd
> > and mirrored...I think reads worked out to be 19MB/s...(bad drives, same
>
> Ah, this would be a RAID 0+1 setup, then? Very different from Jeff's RAID
> 5 configuration. I'd be willing to believe that software RAID 0+1 _could_
> be faster than most hardware (it's just shuffling and dupping blocks
> around to different drives, which could be done with clever pointer
> twiddling) but calculating parity bits in hardware for RAID 5 had got
> to be a win, doesn't it?
>
i would assume that this would be the case. for anybody who is going to
spec a new machine for a database as small as 3-5G, RAID 0+1 has got to
be the choice. i don't have a doubt that it'd be reasonably fast with
software raid. anymore, it'd be hard to buy new disks that small to
build a 0+1 for < 8G (4x4G will give you 8G). when you're on a budget
with a backup server that needs 20+ drives (n+1 for raid5) vs. 40+
drives (2N for 0+1), though, raid 5 is a good solution. doing it again,
i'd go with a hardware controller since no one seems to be refuting my
assumption that the raid5 daemon can suck up a lot of CPU when
calculating parity, even with 2 fairly fast processors.