Re: devices in OST failover

On Mon, 2007-23-04 at 12:56 +0200, Hans Einar Gautun wrote:
> I want to have a local /dev/sdaX on each OST - with same size. That
> means:
> 
> ost1 with its own /dev/sda3
>                              in an active/active failover with
> ost2 with its own /dev/sda3
> 
> Is this possible, or have I misunderstanded something?

The purpose of failover is so that two OSSes can provide the same
service to the lustre network.  That is, should one of the two nodes
fail (i.e. a piano falls on it and completely destroys it), the other
OSS can provide exactly the same services.

So you have to ask yourself, if you have a local disk in each machine
and one machine gets crushed under a piano, how does other machine
provide service from the crushed machine's disk?

There are two solutions.  Use a network replication service like drbd
(so that the contents of the local disks is identical at all times) or
use an external storage system that both OSSes can access, like FC SCSI
or Firewire, etc.

b.