[DRBD-user] Any recommendations or cautions on using RAID under DRBD?

drbd at bobich.net drbd at bobich.net
Tue Mar 4 14:44:21 CET 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 Tue, 4 Mar 2008, Doug Knight wrote:

> Performance is a first priority, followed by
> disk space, so I've been looking at RAID 10 and RAID 50 as possible
> setups. We're planning on using 15K drives, which limits each physical
> drive to 146GB, which is why I need the striping. The controllers will
> have battery backed up cache, which from the postgres groups I've been
> told will give us a significant performance boost.
> The system we're looking at is the Dell PowerEdge 6800, most
> likely with a non-DRBD mirrored system drive, plus a DRBD replicated
> RAID 10 or 50 array supporting around 500GB.

If performance is your 1st priority, then do you really need more than 
RAID 01? Have each machine with a RAID0 stripe (apart from possibly the 
system/root partition), and then mirror it using DRBD (RAID1). RAID 51 
seems a bit OTT if you want performance first, and you'll still get 
mirroring from DRBD.

Just make sure that your bus and controller can keep up with 
the throughput of so many drives. The PCI(X/e/...) bus will only handle so 
much bandwidth, and you are unlikely to see more than 80% of it even under 
optimal conditions. If your drives between them can sustainedly (or 
even just with buffer->controller bursts - new drives have big 
caches!) churn out more than that, then you might as well get 
slower/bigger/cheaper (pick any two ;-) drives.


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