[DRBD-user] Replicating a Boot LUN (root, swap and /boot)

Lars Ellenberg lars.ellenberg at linbit.com
Thu Jul 2 11:26:03 CEST 2009

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

On Tue, Jun 30, 2009 at 02:20:21PM +0000, J R wrote:
> All,
> I have looked around for an answer to this question but haven't found
> one.  The closest configuration to what I need is at:
> http://wiki.openssi.org/go/FC2_DRBD_Root_Failover_HOWTO
> I would like to be able to replicate the Boot LUN (block device) to a
> secondary server.  We presently used array based replication to
> replicate our Boot from SAN (fiberchannel) servers so we can boot them
> up at an alternate location for DR.  There have been challenges when
> moving from QLogic Failover Multipathing to native DM-MPIO
> multipathing due to reliance on WWID and other issues with the non LVM
> native EXT3 /boot partition.
> That being said, I am interested with this as a low cost alternative
> for our remote sites to use internal storage while providing a very up
> to date (asynchronous) copy of the Boot LUN.

What for?
Latest / from SAN, but arbitrarily old /data/ from local storage?
Use case?
How often do you expect the content of your / to change?
Why would you think you need DRBD to replicate this mostly static data?

> I am not looking to automate the failover (via heartbeat, RHEL
> clustering, etc.) but thought I would create another disk to an
> already running server to be the target of the Boot LUN replication
> (secondary).

Could you make a sketchy drawing of that?  ASCII art maybe?
And the various stages of how you'd want to use it?

> Is this possible?

And it gives you plenty oportunities to hurt yourself.

> Is there any documentation describing how to accomplish this (ie -
> mkinitrd with the appropriate kernel mods?

No. And don't ask me about it ;)
This is simply not the purpose of DRBD.
Integrated in OpenSSI, it did make sense.
But I simply fail to understand your use case.

> The Boot LUN would contain the standard root "/" file system via LVM,
> swap via LVM and /boot as native ext3 partition.

I know you hate being told that what you think you want to do
is not really what you want to do, actualy ;)

But you really do not want to replicate your root via DRBD.
You simply do not want to do that. Really.

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

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