[Beowulf] Re: SATA or SCSI drives - Multiple Read/write speeds.

Robert G. Brown rgb at phy.duke.edu
Tue Dec 9 12:49:26 EST 2003

On Tue, 9 Dec 2003, Robin Laing wrote:

> I agree but I am not looking at swap thrashing in the sense of many 
> small files.  I am looking at 1 or 2 large files that are bigger than 
> memeory while working.  I know on my present workstation I will work 
> with a file that is 2X the memory and I find that the machine stutters 
> (locks for a few seconds) every time there is any disk ascess.  I 
> would like to add more ram but that is impossible as there are only 
> two slots and they are full.  Management won't provide the funds.

I have to ask.  Is it a P4?  Strictly empirically I have experienced
similar things even without filling memory.  I actually moved my
fileserver off onto a Celeron (which it has run flawlessly) because it
was so visible, so annoying.

I have no idea why a P4 would behave that way, but to my direct
experience at least some P4-based servers can be really BAD on file
latency for reasons that have nothing to do with the disk hardware or
kernel per se.  Maybe some sort of chipset problem, maybe related to the
particular onboard IDE/ATA controllers -- I never bothered to try to
debug it other than to move the server onto something else where it
worked.  AMD or Celeron or PIII are all just fine.

If you're stuck on the hardware side with no money to get better
hardware, well, you're stuck.  My P4 system had plenty of memory and a
1.8 MHz clock and still was a pig compared to a 400 MHz Celery serving
the SAME DISK physically moved from one to the other.


Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu

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