[TriLUG] NFS write performance problem

[Scott Stancil]

I am having NFS write performance issues with a backend dedicated NFS
server (RedHat 8.0, PIII 550, 128MB ram, 100Mbps network).  The client (RH
6.1, Kernel 2.2.19SMP with nfs-utils-0.1.9.1-1, dual PIII 550's, 1GB ram,
100Mbps network) is mounting the home directory off of the server. 
Integrated Intel EtherExpress 100 ethernet devices on both.

Testing Methods:
I am using the following to test the network transfers from the client to
the server.
 Write:
 time dd if=/dev/zero of=/mnt/home/testfile bs=x count=y

 Read:
 time dd if=/mnt/home/testfile of=/dev/null bs=x


Results:
Unmounts between changes to clear caching. Reading and writing a 262MB file.

X=8 Y=32768, Write=2:48, Read=0:10, 1.55 MB/second, 24.25MB/second read

X=16 Y=16384, Write=2:48, Read=0:25, 1.55 MB/second write, 10.5 MB/second

read X=32 Y=8291, Write=2:48, Read=0:15, 1.55MB/second write, 17.5
MB/second read


Hard drive settings:

RAID 1 EIDE drives are showing the following with "hdparm -Tt /dev/hda".

/dev/hda:
 Timing buffer-cache reads:   128 MB in  1.33 seconds = 96.24 MB/sec
 Timing buffered disk reads:  64 MB in  1.39 seconds = 45.96 MB/sec

/dev/hdc:
 Timing buffer-cache reads:   128 MB in  1.33 seconds = 96.24 MB/sec
 Timing buffered disk reads:  64 MB in  2.31 seconds = 27.68 MB/sec

This doesn't suprise me as I suspect that the secondary controller is not
quite as fast as the primary controller, but still well above the read
bottleneck.

hdparm <device>:

/dev/hda:
 multcount    = 16 (on)
 IO_support   =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 readonly     =  0 (off)
 readahead    =  8 (on)
 geometry     = 4865/255/63, sectors = 78165360, start = 0

/dev/hdc:
 multcount    = 16 (on)
 IO_support   =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 readonly     =  0 (off)
 readahead    =  8 (on)
 geometry     = 77545/16/63, sectors = 78165360, start = 0


Although this is a test server and I can mess with it as much as I want, I
would prefer not to perform a reinstall if at all possible. :)

1.  I have examples of testing reads from the disk performance, but what
might I use to test writes, especially to a RAID 1 slice/partition?
2.  Geometry is "off" in /dev/hdc or is it?  It has worked without
complaint for about a month now, but they are identical disks and the
geometry is way off.  Could the difference in controllers cause this?
3.  Anyone have any ideas on how to improve the pitiful write performance?
Or perhaps how to benchmark/troubleshoot my performance a little better?

-- 
Scott Stancil
sstancil at geekrooms.com