[ClusterLabs] DRBD or SAN ?

Dmitri Maziuk dmaziuk at bmrb.wisc.edu
Tue Jul 18 04:08:45 EDT 2017

On 7/17/2017 2:07 PM, Chris Adams wrote:

> However, just like RAID is not a replacement for backups, DRBD is IMHO
> not a replacement for database replication.  DRBD would just replicate
> database files, so if for example file corruption would be copied from
> host to host.  When something provides a native replication system, it
> is probably better to use that (or at least use it at one level).

Since DRBD is RAID-1, you need double the drives either way, no 
advantage over two independent copies -- only the potential for 
replicating errors. You probably need a 10G pipe, with associated costs, 
for "no performance penalty" DRBD while native replication tends to work 
OK over slower links.

At this point a 2U SuperMicro chassis gives you 2 SSD slots for system 
and ZiL/L2ARC plus 12 spinning rust slots for a pretty large database...

That won't work for VM images, for that you'll need NAS or DRBD but IMO 
NAS wins. Realistically, a hard drive failure is the most likely kind of 
failure you're looking at, and initiating a full storage cluster 
failover for that is probably not a good idea. So you might want a 
drive-level redundancy on at least the primary node, at which point 
dual-ported SAS drives in external shelves become economical, even with 
a couple of dual-ported SAS SSDs for caches. So ZFS setup I linked to 
above actually comes with fewer moving parts and all the handy features 
absent from previous-gen filesystems.


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