Three Little Words
PVN? USN? Who was right?
- By Dian Schaffhauser
- February 01, 2001
The argument started this way: Two manuscripts
came in, both from excellent writers who understand
Microsoft technology, possess MCSE titles, work
with Windows 2000 on a regular basis, and have
fairly deep knowledge of Active Directory. First,
we worked on Curt Simmons’
story on intra-site AD replication. Then we
tackled Jeremy Moskowitz’s
article on bringing AD accounts back once
they’ve been lost. It’s when we were looking over
the polished results that we realized something
Both writers allude to the approach AD uses to
keep track of the currency of its objects. AD
uses an approach involving a combination of USNs
(update sequence numbers) and PVNs (property version
numbers). The two stories we had on hand appeared
to contradict each other in how these two types
of identifiers work.
In an effort to reach agreement, we questioned
both writers, who dug in their technologist heels.
Jeremy’s explanation: “USNs are to check out for
when ‘things are in sync,’ and PVNs check out
‘what needs to be updated.’” Curt concluded: “What
[sources] I’ve found always seem to talk about
USNs in terms of replication and PVNs in terms
of collision resolution.” Well, that certainly
cleared things up.
Then they upped the ante. Jeremy quoted his technical
mentor, Bill Boswell, esteemed author of Inside
Windows 2000 Server from New Riders. Curt cited
the Active Directory Technical Reference from
So we editors did as we’ve always done: We kept
asking questions — in this case, of Microsoft.
We turned to Waggener Edstrom, Microsoft’s primary
PR company. Lisa answered the phone. That’s when
I whispered those three little words: “USN or
The publicist kicked into action. We exchanged
daily e-mail for at least a week as she attempted
to track down the final authority on AD. Apparently,
that person must be at work on Blackcomb’s directory
structure behind a locked door. The e-mail updates
petered out. We were back where we started.
By now, it was just a matter of a few days before
the issue went to the printer. What to do? Hold
the stories until we could be absolutely positive
of their accuracy? That would leave a few blank
pages. Publish them as they were written and hope
nobody noticed? Once a reputation for technical
veracity is lost, it’s tough to win back. Besides,
if ever I’ve seen an eagle-eyed readership, you’re
it. You’d notice.
That’s when Mr. Boswell came to our rescue. He
suggested that he write a sidebar explaining these
two concepts. This offer arrived — like the cavalry
— at the last possible minute, and I know he worked
evenings and a weekend to pull it together in
time. You’ll find Bill’s
article in our online edition of this issue.
We’ve left the articles by Curt
and Jeremy intact.
Do both authors have it right? Is anybody wrong?
Weigh in at email@example.com.
Dian L. Schaffhauser is a freelance writer based in Northern California.