[DRBD-user] Trouble getting RAID5 on top of DRBD to work..

Stefan Seifert nine at detonation.org
Fri May 30 12:55:29 CEST 2008

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

On Friday, 30. May 2008, drbd at bobich.net wrote:
> I think you'll find that you are. With RAID 51, you can lose up to 1 disk
> per side. With RAID 15 you could lose all disks on one side without even
> needing to fail over to the backup node.

If you could lose all disks on one side in a RAID 15 without having to fail 
over, why would you need to failover if one of the RAID 5s in a RAID 51 fails 
due to two drives failing?

> RAID isn't about speed, it's about fault tolerance, and RAID 15 is more
> fault tolerant than RAID 51.

So in your RAID 15 you lose two hard drives of one node and before being able 
to replace it the other node goes down because of a failing power supply or 
whatever. Your cluster's down.
On RAID 51 you lose two hard drives of one node and then the other node goes 
down. Your cluster's down, too. No difference here.

I've played it through with many other cases. In each of them I get exactly 
the same characteristics. The only difference is wether the RAID 1 or RAID 5 
fails first which makes no difference at all on the cluster's status.


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