[DRBD-user] Performance Issues on version 8.3.13

Lars Ellenberg lars.ellenberg at linbit.com
Thu Apr 25 22:33:00 CEST 2013

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

On Thu, Apr 25, 2013 at 06:07:52PM +0200, GG-Net Mailing wrote:
> Hey there,
> the speed is significatnly higher due to the Samsung 840 SSD's
> performance plus the performance of the raid controller.

Why would you want to combine a SSD Primary
with single-sindle HDD Secondary?

> And according to you, if I use protocol A or C is pretty much
> irrelevant to the performance of the DRBD, since it's always only as
> fast as the slowest node?

Protocol A changes the latency of the single IO, and is effective mainly
if the working set is typically covered by the activity log, but you
have a high latency link (or secondary IO subsystem).

It is unlikely to have much impact on sustained throughput
 (how could it; replication bandwidth is still the same)
or on sustained strictly random write IOPS,
as under continuous load you will still hit congestion.

If you have a slow link, or slow Secondary IO subsystem,
protocol A (or taken further, DRBD-Proxy) cannot improve
*sustained* IOPS under continuous heavy load. 
They can "hide" load peaks, and reduce average latency.

Maybe these posts (some ascii art) help:

Also have a look at

Or in short:
Don't think you can get away with a crappy secondary
because you "won't ever need it anyways"...

High performance primary + crappy secondary
results in crappy overall system.

(except in a few very specific use cases)

Also, DRBD is primarily to enable failover.
To avoid a lot of pain in the failover scenarios,
all nodes in a failover cluster should be equally powerful.


: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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