[DRBD-user] Clarification on How-To

Nuno Tavares nunotavares at hotmail.com
Fri Sep 17 03:06:34 CEST 2004

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

Alan and John,

This is *NOT* true, at least for 0.6.x. I'm still lacking the time to test 
0.7.x though.

DRBD has (used to have?) a legacy mode, which will boot DRBD devices as 
Secondary, leaving the decision of whom is Primary (the to-be-mirrored 
device) to Heartbeat (or another cluster manager). There are situations when 
the DRBD switches need to be controlled externally, thus (of course) 
compromising the latest-data-availability.

This setup has been working for several weeks, and its described in my 
LTSP-HA HOWTO[1]. See chapter 4.1.2 for further explanation - it was 
discussed in this list at the time of writing.

Best regards,

[1] http://republico.estv.ipv.pt/~nmct/ltsp/ha/
Nuno Tavares

>From: Alan Robertson <alanr at unix.sh>
>To: Nuno Tavares <nunotavares at hotmail.com>
>CC: drbd-user at linbit.com
>Subject: Re: [DRBD-user] Clarification on How-To
>Date: Thu, 16 Sep 2004 14:34:03 -0600

>Nuno Tavares wrote:
>>>From: Alan Robertson <alanr at unix.sh>
>>>To: John Lange <john.lange at bighostbox.com>
>>>CC: drbd <drbd-user at linbit.com>
>>>Subject: Re: [DRBD-user] Clarification on How-To
>>>>Since the config files is not designed to indicate a primary node, how
>>>>does drbd know which node shoul
>>Each DRBD device keeps an internal state which will allow to determine 
>>which one is the most up-to-date (should read last-changed) node, between 
>>the two hosts connecting. This way the DRBD will always know which is the 
>>*best* DRBD to mirror from.
>>You can surpass this behaviour by using a cluster manager (like 
>>Heartbeat), or doing it manually using drbdadm/drbdsetup.
>DRBD will never knowingly use out of date, and heartbeat will not override 
>that.  Only humans can override that IIRC.  On older implementations it 
>will refuse to fail over to the side with old data.  On recent versions, it 
>will allow updates from either side, but it still uses the best copy of the 
>data (until they are updated to be the same).
>     Alan Robertson <alanr at unix.sh>
>"Openness is the foundation and preservative of friendship...  Let me claim 
>from you at all times your undisguised opinions." - William Wilberforce
>drbd-user mailing list
>drbd-user at lists.linbit.com

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