[DRBD-user] noobie question

Lars Ellenberg lars.ellenberg at linbit.com
Mon Apr 6 20:07:35 CEST 2015

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

On Sun, Apr 05, 2015 at 12:10:20AM -0500, Bruce Goldstein wrote:
> Hello and sorry for the basic question.  I see how the replication works
> with DRBD.  My question has to do with how servers that are accessing the
> primary SAN can then access the secondary SAN when a failover occurs.  In
> network routing, we use VRRP or similar to access the current primary
> device. How does this work in DRBD?  Thanks in advance.

DRBD does "just" data replication.  No more, no less.

Which means you usually need some sort of cluster manager and other "glue"
to actually make use of it.

One typical use case is to have DRBD mounted locally directly on
the current "Primary", and run some service (say, apache, or postgres)
using data stored in that file system.
Clients would access this service through a dedicated service IP.

Pacemaker (our preferred cluster manager) would then decide when to take
action, when and where to promote DRBD, mount the file system, start the
service, and make that IP available.

Other use cases include Virtualization (the "service" to start would be
the virtual machine), or exporting DRBD via NFS, Samba, iSCSI or other
protocols, but again Pacemaker would decide when and where to place the
services, and access is typically via some dedicated service IP,
placement of which is again controlled by Pacemaker.

: Lars Ellenberg
: http://www.LINBIT.com | Your Way to High Availability
: DRBD, Linux-HA  and  Pacemaker support and consulting

DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.

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