[DRBD-user] Suggestion for DRBD User's Guide

drbd at bobich.net drbd at bobich.net
Wed Mar 12 16:38:34 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 Wed, 12 Mar 2008, Whit Blauvelt wrote:

>>> My initial impression, having not seen this complete yet, is that this is
>>> running a lot slower than, say, rsync would in duplicating the same amount
>>> of data. Doubtless drbd has more to do. Anyway, it would be helpful if the
>>> manual gave a rough formula for guestimating sync time.
>> Added to the to-do list. Not sure whether it will be in the changeset for 
>> next week though.
> Here's an additional question the manual might answer: Are the subsequent
> operations as slow as the initial sync? Or do they runs at something closer
> to normal file transfer speed? In our case what I'm trying to test it for is
> a 60 gig partition. It's been running the initial sync for a day, and looks
> to have another day to go. This is between one gig NICs, between top-end HP
> boxes. It will be really useful if drbd is capable in this circumstance. But
> if putting a new 2 gig file onto the primary device results in a sync this
> slow - it's roughly taking about an hour to sync a single gig on the initial
> pass here - then drbd makes no sense compared to running rsync at regular
> intervals.

No, it's not supposed to be that bad.

What version of DRBD are you using? What does drbd.conf say? Have you verified 
latency and throughput on your Gb interfaces independently of DRBD? Have you 
verified idle sync speed with no other operations happening on the DRBD devices 
(without them being mounted)? What does /proc/drbd say it's speed is? What 
distro are you using? Did you compile from source or get the rpms from a 

> Since I won't be able to test operational transfer speed in this setup until
> tomorrow, I just don't know. But the manual should tell me, before I get
> myself into a situation where I'm waiting for a couple of days just to do
> the feasibility test. Is drbd useful only for very small devices or devices
> in minimal use? I'm guessing not, since I've seen no upfront warning that
> this is the case.

No, I've tested it with devices/volumes up to hundreds of GB. One thing that 
did cause me problems is an upgrade from 8.0.8 to 8.0.11+, though. The 
performance went through the floor, probably to similar levels that you are 
seeing. I'm back to 8.0.8 and it's all working happily again. What version of 
DRBD are you running? Try downgrading to 8.0.8 (including the kernel module) 
and see if the problem goes away.


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