[DRBD-user] allow-two-primaries (hot migration) and three nodes...
stef at genesix.org
Sat Dec 12 22:51:48 CET 2020
Hi Anthony, Hi Gianni,
At first thanks for your friendly advices.
And I confirm I'm new in today hot migrating fields :) More precisely
I've done some successful experiments almost ten years ago with xen drbd
and remus (true HA). Very resource-intensive but also an interesting
I've carefully checked each migrating steps with "drbdadm status
To my understanding and observations (feel free to correct me) :
- The parameter "allows two primaries" is just a right to use two
primaries at the same time, not a constant state with two primaries on.
- I always only saw one primary at a time on the three servers.
- When I launch a "xl migrate <domu> <destination_server>" a xen/drbd
script is executed to manage (among others things) the primary state on
<destination_server> when necessary.
I confirm I don't have to "drbdadm primary <drbd-volume>" on
<destination_server> before a "xl migrate <domu> <destination_server>"
I migrate many times a test instance to server 1 > server 2 > server 3 >
server 1 > server 2 > again and again with, a the same time a simple
process running inside the instance and outputting text on a console.
Le 12/12/2020 à 20:47, Gianni Milo a écrit :
> AFAIK the recommendation is to have dual primary mode enabled _only_
> during the live migration stage and once that's completed, one must
> revert back to the single primary mode. Linbit folks have multiple times
> warned against using _permanently_ dual primary mode for obvious to
> me reasons.
Sounds logical. Very hazardous. I understand that a "drbdadm primary
<drbd-volume>" is like a mount with r/w rights.
The management of drbd and migrations is done only with scripts. So I
hope to have a correct, error-free process. It's a hope, not a certainty :)
Ile d'Oléron - France
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