Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
/ 2005-06-23 09:19:02 +0200 \ Martin Bene: > > I'm testing and tinkering with DRBD to answer all those 'what if' > > questions before we go into production. While doing this I managed > > to get a node into the state where it is the Primary and the > > SyncTarget at the same time. > > > > This has got to be a bad thing if you try to mount the FS as > > the data > > under the fs will change as the sync progresses, right? I see a > > great opportunity for data corruption here. > > > > So, is there a reason why this is even allowed by drbd? I can't see > > a situation where it would be needed, does such a situation exist? > > That's a feature, you don't risk data corruption. > > In previous versions sync target/source was coupled with > primary/secondary state. On boot, this required waiting for all sync > operations to finsih before starting heartbeat (or whatever cluster > manager you use) so heartbeat could freely choose which devices to make > primary. > > With current drbd, this restriction no longer applies, startup can > continue right after connecting the drbd devices. > > If you make a sync target primary, all reads for out-of-sync data are > fetched from the sync source, so the data read off the drbd device stays > consistent. Especially in an active/active cluster with multiple drbd > devices this greatly reduces risk of long startup delays. Thank you, Martin :) Only to state it again explicitly: You can only reach the state "SyncTarget and Primary", if it _was_ Secondary, and target of sync already, and you (or some cluster manager) promote it to Primary. When a running Primary suddenly shall become SyncTarget, [which can only happen after split brain or "operator error",] it will refuse to do so, and drop the connection to the peer (--> StandAlone) [to avoid data corruption] -- : Lars Ellenberg Tel +43-1-8178292-0 : : LINBIT Information Technologies GmbH Fax +43-1-8178292-82 : : Schoenbrunner Str. 244, A-1120 Vienna/Europe http://www.linbit.com : __ please use the "List-Reply" function of your email client.