Paul,
We've just upgraded our main filers to 7.0.5 after running 588 days with no interruption on 6.5.5. However we've run into serious problems when enabling quotas. The system runs at 100% for ages and we eventually have to disable quotas altogether.
We had similar problems when we upgraded from 6 to 7.0.2 in Oct 2005. It took several attempts to initilize quotas and when we finally managed it, it took 47 hours over a quiet weekend.
It took a while to get a useful response from Netapp, but they finally suggested putting default tracking quotas at the top of the quota file of the form:
* user@/vol/<volname> - - * group@/vol/<volname> - - * tree@/vol/<volname> - -
Our user filestore is on vol4, so we used:
QUOTA_PERFORM_USER_MAPPING on * user@/vol/vol4 - - * group@/vol/vol4 - - * tree@/vol/vol4 - - #--normal quota entries below here----
and this improved things. The quotas initilaised 3 times faster than the first attempt and the filer happily served data during the initialisation. Once done, you only need to do a quota resize to update the quotas, which takes a couple of minutes.
Last time I did a quota initilisation on our user filestore (also ~20,000 users and similar setup to yours) it only took 10 hours, that is also with 7.0.5.
I'd be happy to discuss this further with you off-list if you want.