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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