[DRBD-user] performance issues with DRBD :(

Florian Haas florian.haas at linbit.com
Thu Dec 10 16:58:01 CET 2009

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

Lars beat me to this but anyway...

On 2009-12-10 13:23, Beck Ingmar wrote:
> Hi Florian,
> why improves bonding of the replication-connection not the performance.

I did not say that. :) I said round-robin bonding _over 4 NICs_ would be
detrimental to performance.

> We currently have a direct connection for the 1 Gb DRBD replication and
> I
> wanted to activate an active-active bonding (with a further LAN-port). I
> would expect nearly double of replication-performance.

All of the following applies to DRBD Connected in protocol C:

- With 1 GBit Ethernet link, you can do about 110 MB/s (provided your
storage subsystem has that bandwidth);

- With 2 GBit links bonded in round-robin mode, you top out at around
160-170 MB/s (even then you may have to tune kernel TCP parameters);

- with 3 Gbit links, your throughput will drop down to around 110 MB/s;

- with 4 links or more, you will get _significantly less_ throughput
than a single unbonded link.

Reason for all this: TCP reordering.

> Or depends it on whether the connection between the nodes directly or
> via 1-n switches.

I am talking about back-to-back connections. Switches could make it worse.


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