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

drbd at bobich.net drbd at bobich.net
Mon Jun 2 16:43:14 CEST 2008


On Mon, 2 Jun 2008, Sören Malchow wrote:

> i did not try that before ( with RAID 6 ) but may i suggest using CLVM together with the
> Redhat Cluster Suite on top of DRBD, put both drbd nodes in primary and run a cluster with
> GFS2 on top of that.

1) What is the purpose of (C)LVM in this setup? LVM for the sake of LVM 
seems to be rather common these days.

2) This won't provide the sort of redundancy that we discussed. RAID 15 is 
some orders of magnitude better than RAID51 in this regard. If you have 
two lots of hardware RAID5 mirrored, that's RAID51.

> That should do the Job, we have a setup like that running with plain ( no RAID ) lvm volumes,
> since we have a hardware RAID

The suitability of that depends on what the use case is. If latency on 
lots of small files is important, fail-over likely wins over 
primary/primary with a cluster FS. If you need throughput on large files, 
then load balancing a couple of primary/primary machines may well come out 
ahead. But one is not obviously better than the other - it depends on what 
you are intending to use it for.

And it still doesn't get away from the fact that RAID15 is better than 
RAID51.

My gut feeling is that the problem with md on top of DRBD in fail-over 
mode seems to have something to do with the md signatures, but I don't 
have a pair of machines to try this on at the moment.

Gordan


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