heavy NFS writes lead to corrup summary in superblock

[Mikhail Teterin]

Our amd64 6.1-STABLE system is used to collect backup dumps from production 
systems (mostly -- Solaris) via NFS. When in progrss, the dumps arrive at an 
average rate of 20Mb/s.

Every once in a while I notice a discrepancy in the amount of used space on 
the backup FS as reported by df vs. that reported by the total du.

Unmounting the FS and fsck-ing it fixes the problem with fsck reporting 
(despite the clean unmount):

	SUMMARY BLK COUNT(S) WRONG IN SUPERBLK
	SALVAGE? yes

The FS is intended for very few very large files and was created 
with "newfs -b 65536 -O1" (no softupdates).

This workaround (explicit fsck) is acceptable for us, but it is a sign of some 
kind of rot, and I thought, you'd like to know...

Yours,

	-mi