SCSI drives recommendations

Steven Hanley sjh at
Tue Jan 22 09:15:06 EST 2002

On Mon, Jan 21, 2002 at 11:15:04AM -0000, Richard Cottrill wrote:
> I think that kind of misses the point of what I was getting at. RAID5 is
  good for making a big, reliable volume. It is not, however, very good at
  'fast'. On a volume with many discs RAID5 is much more efficient (in terms
  of capacity) than simple mirroring; but not as fast (those parity values
  need to be calculated).

I dont know that the calculation of parity is a slow down, I notice that when
you insmod the raid5 module it does some tests with different code to see what
speed it can do the parity calculations at.

kernel: raid5: measuring checksumming speed
kernel:    8regs     :   832.000 MB/sec
kernel:    32regs    :   392.000 MB/sec
kernel:    pII_mmx   :  1014.000 MB/sec
kernel:    p5_mmx    :  1061.200 MB/sec
kernel: raid5: using function: p5_mmx (1061.200 MB/sec)
(from a dual 550 machine)

so if the cacuations are happening even at a 10th the speed of this
calcualtion there is no chance that that would be slowing things down.

        See You

sjh at
Look Up In The Sky
    Is it a bird?   No
        Is it a plane    No
            Is it a small blue banana?

More information about the linux mailing list