[DRBD-user] documentation clarification - Generation Identifiers

Jonathan Woodbury jpwoodbu at google.com
Thu May 30 23:52:45 CEST 2013

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

Hi there,

In reading this page (http://www.drbd.org/users-guide-8.3/s-gi.html) your
online docs, in the "How DRBD uses generation identifiers" -> #5 "Current
UUID matches peer's historical UUID" section, I found something a bit
confusing and I'm suspicious that it may be incorrect.

It states:

"The local node detects that its current UUID matches one of the peer's
historical UUID's. This implies that while the two data sets share a common
ancestor, and the local node has the up-to-date data, the information kept
in the local node's bitmap is outdated and not useable. Thus, a normal
synchronization would be insufficient. DRBD now marks the entire device as
out-of-sync and initiates a full background re-synchronization, with the
local node becoming the synchronization source."

If the local node's current UUID matches one of the peer's historical UUIDs
wouldn't that mean that the local node's data is an older generation than
the peer's and the local node's data should be considered out-of-date and
replaced with the peer node's data?

Also, thanks for providing and hosting these high quality docs!  I hope
that this discussion can serve to help make them even better or set me
straight ;)

Jonathan Woodbury
Ganeti SRE - NYC
Google Inc.
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