NFS server usage

[Charles Swiger]

On Feb 26, 2004, at 4:57 PM, Michael Conlen wrote:
> [ ... ]
> The production system will use dual channel U320 RAID controllers with 
> 12 disks per channel, so disk shouldn't be an issue, and it will 
> connect with GigE, so network is plenty fine, now I'm on to CPU.

Sounds like you've gotten nice hardware.  Four or so years ago, I built 
out a roughly comparible fileserver [modulo the progess in technology 
since then] on a Sun E450, which housed 10 SCA-form-factor disks over 5 
UW SCSI channels (using 64-bit PCI and backplane, though), and could 
have held a total of 20 disks if I'd filled it.  I mention this 
because...

> Low volume tests with live data indicate low CPU  usage however when I 
> best fit the graph it's dificult to tell how linear (or non linear) 
> the data is. [ ... ] Does that kind of curve look accurate to you 
> (anyone)?

...even under stress testing on the faster four-disk RAID-10 volume 
using SEAGATE-ST336752LC drives (15K RPM, 8MB cache), each on a 
seperate channel, with ~35 client machines bashing away, the fileserver 
would bottleneck on disk I/O without more than maybe 10% or 15% CPU 
load, and that was using a 400MHz CPU.

The notion that an NFS fileserver is going to end up CPU-bound simply 
doesn't match my experience or my expectations.  If you have 
single-threaded sequential I/O patterns (like running dd, or maybe a 
database), you'll bottleneck on the interface or maximum disk 
throughput, otherwise even with ~3.5 ms seek times, multi-threaded I/O 
from a buncha clients will require the disk heads to move around so 
much that you bottleneck at a certain number of I/O operations per 
second per disk, rather than a given bandwidth per disk.

-- 
-Chuck