On 2018-10-18 4:00 p.m., Lars Ellenberg wrote: > On Wed, Oct 17, 2018 at 03:11:42PM -0400, Digimer wrote: >> On 2018-10-17 5:35 a.m., Adam Weremczuk wrote: >>> Hi all, >>> >>> Yesterday I rebooted both nodes a couple of times (replacing BBU RAID >>> batteries) and ended up with: >>> >>> drbd0: Split-Brain detected but unresolved, dropping connection! >> >> Fencing prevents this. >> >>> on both. >>> >>> node1: /drbd-overview// >>> //0:r0/0 StandAlone Primary/Unknown UpToDate/DUnknown /srv/test1 ext4 >>> 3.6T 75G 3.4T 3% / >>> >>> node2: /drbd-overview // >>> //0:r0/0 StandAlone Secondary/Unknown UpToDate/DUnknown/ >>> >>> I understand there is a good chance (but not absolute guarantee) that >>> node1 holds consistent and up to date data. >>> >>> Q1: >>> >>> Is it reasonably possible to mount /dev/drbd0 (/dev/sdb1) on node2 in >>> read only mode? >>> >>> I would like to examine the data before discarding and syncing >>> everything from node1. >> >> Yes. You can also promote node 2 to examine it as well. >> >>> /drbdadm disconnect all// >>> //drbdadm -- --discard-my-data connect all/ >> >> Discarding the data will trigger a resync and resolve the split-brain, >> but of course, any changes on the discarded node will be lost. >> >>> Q2: >>> >>> Will the above completely purge all data on node2 or just drbd metadata? >>> >>> I.e. will all 75G have to be fully copied block by block or a lot less? >> >> It will do a full resync. > > Even after a "split brain" (rather: data divergence), > DRBD usually can do an "incremental, bitmap based" resync: > DRBD knows which blocks have changed on each node, and will sync the > blocks described by the bit-or of those out-of-sync bitmaps.
Glad to hear I was wrong on that, cool. >>> I'm concerned about time and impact on performance when it comes to >>> terabytes of data. >>> >>> Regards, >>> Adam >> >> The resync (on 8.4) adapts the resync rate to minimize impact on >> applications using the storage. As it slows itself down to "stay out of >> the way", the resync time increases of course. You won't have redundancy >> until the resync completes. -- Digimer Papers and Projects: https://alteeve.com/w/ "I am, somehow, less interested in the weight and convolutions of Einstein’s brain than in the near certainty that people of equal talent have lived and died in cotton fields and sweatshops." - Stephen Jay Gould _______________________________________________ drbd-user mailing list [email protected] http://lists.linbit.com/mailman/listinfo/drbd-user
