Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
/ 2007-02-12 12:59:13 -0500 \ Ross S. W. Walker: > > > What is the down side to increasing al-extends, just longer > > re-syncs? > > > > longer resyncs in case of primary crash. > > Oh, so if the replica is disconnected and standalone, then when the > secondary re-connects what happens then if the data written on the > primary is > then al-extends? there is probably a misconception about what those "al-extends" are. we have a "dirty bitmap", which tracks, well, "dirty" blocks, where dirty is: modified locally and not mirrored. AND we have the activity log (the size of which gets tuned with the al-extends parameter). this tracks _active_ extends, that is extends to which io may be "on the fly". in case we recover from a primary crash, we have no way to know whether the "in flight" io has made it to (which) disk. so for all extends covered by the activity log, we flag the corresponding bits in the bitmap as "dirty". upon resync, the bitmaps of the nodes get ORed together, and the blocks corresponding to dirty bits get resynced. > > > Does all data covered in al-extends get re-synced? > > > > after a primary crash :) > > Only after a crash? What about after a disconnect and re-connect? whenever necessary, we resync the changed blocks. when you just disconnect/reconnect, the activity log is not involved. ... > So we would tell heartbeat that if we are not primary to not auto-start > drbd, just hang out until further notice, for if it is scheduled > replication we will be handling this through cron script. Only if we are > primary do we need to start drbd. If I'd have scheduled replication, I'd not involve heartbeat in any way. I would feel very bad about automating a failover to stale data. -- : Lars Ellenberg Tel +43-1-8178292-0 : : LINBIT Information Technologies GmbH Fax +43-1-8178292-82 : : Vivenotgasse 48, A-1120 Vienna/Europe http://www.linbit.com : __ please use the "List-Reply" function of your email client.