Why does RHEL6.3 generate significantly more calls via NFS than SuSE 10.2 when measured by 'du' or 'dd'?

Issue

• Slower NFS performance on RHEL6.3 when comparing it to SLES 10.2
• The slowdown is being quantified by two different types of tests that represent two different types of NS operations:
  1. a dd of a 2GB file to the share (Which shows a WRITE of a large file):

# time dd if=/dev/zero of=/export/subdirectory/test.dd bs=4M count=250 conv=fsync oflag=direct)

2. a du -sh ran against files within the share (Which shows a GETATTR of a large number of files within a directory):

# time du -sh /export/subdirectory

• With attribute caching enabled (mount option actimeo set to non-zero value) the du times are in line with each other on both platforms and the dd times are about 10 seconds faster on SLES then RHEL
• When attribute caching is disabled the du times are about 2x longer on RHEL then on SLES and the dd times are faster on RHEL.