"Christopher E. Brown" wrote:
> On Thu, 4 May 2000, Michael Robinton wrote:
> > >
> > > Not entirely, there is a fair bit more CPU overhead running an
> > > IDE bus than a proper SCSI one.
> >
> > A "fair" bit on a 500mhz+ processor is really negligible.
>
> Ehem, a fair bit on a 500Mhz CPU is ~ 30%. I have watched a
> *single* UDMA66 drive (with read ahead, multiblock io, 32bit mode, and
> dma transfers enabled) on a 2.2.14 + IDE + RAID patched take over 30%
> of the CPU during disk activity. The same system with a 4 x 28G RAID0
> set running would be < .1% idle during large copies. An exactly
> configured system with UltraWide SCSI instead of IDE sits ~ 95% idle
> during the same ops.
Can I inquire as to how you are checking the CPU utilization? I have a
200 Mhz K6 with both IDE and SCSI drives running raid0. Bonnie results on
both the IDE raid array, and the SCSI array show very low cpu usage, less
than 2%. This is on a HX motherboard that doesn't support UDMA in the
bios (PIO Mode 4 max). DMA is enabled in Linux though. Accually the
1.3GB maxtor ide drive in bonnie is FASTER than a Quantum 2.1GB SCSI
(sym53c8xx drv) when tested in non-raid. I have two of those 2.1GB in
raid0, so the SCSI array is faster overall of course.
On a second line of thought, RAID cpu overhead seems really low. When I
wanted more space on the 1.3GB maxtor, I added another IDE drive (fairly
old 540 meg) in a linear array (since its slower than the maxtor raid0
would be stupid) along side the 1.3. A bonnie test comparing the 1.3
single to ( 1.3 + .5 ) with raid linear shows some test slower by about
5%, and some faster by about 5%. I realize the bonnie test was mainly
writing to the 1.3, however it has to go through the raid layer as well.
This tells me that appending drives (even if slower) to give more space
doesn't affect performance (much) compared to the single drive.
One more question I have is how do you tell how much cpu time something
compiled into the kernel is using ( ie masquerade, scsi driver, etc ) or
as a module ( ie bridge etc ). Top seems to show only userspace
programs. Is there anyway to check a certain driver compiled into the
kernel?
A little of topic, but oh well...
