SCSI drives recommendations
sjh at wibble.net
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.
sjh at wibble.net http://wibble.net/~sjh
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