[DRBD-user] Limiting the DRBD resync speed

Lars Ellenberg lars.ellenberg at linbit.com
Tue Sep 11 10:44:59 CEST 2012

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, Sep 06, 2012 at 04:26:30AM -0700, lucas.l wrote:
> Hello,
> we've got a drbd-8.4.1 installation running in a custom HA setup. The
> controllers are connected via a 100M Ethernet link with an Ethernet
> switch. In order to keep our services responsive, we need to keep the
> resources' usage low during initial/full synchronization. We've tried
> a fixed resync-rate as well as the dynamic sync rate controller to set
> the maximum resync speed at 1M. We also gave drbd-8.4.2rc3 a try and
> still failed to achieve the goal. Here is our DRBD configuration:

> # cat /proc/drbd
> version: 8.4.2rc3 (api:1/proto:86-101)
> GIT-hash: f25fbeaaf922cb91e33a9c2eb99560473b0b2122 build by build at lnxdev, 2012-09-05 15:40:38
> (...)
>  5: cs:SyncTarget ro:Secondary/Primary ds:Inconsistent/UpToDate C r-----
>     ns:0 nr:38912 dw:38912 dr:0 al:0 bm:5 lo:0 pe:0 ua:0 ap:0 ep:1 wo:d oos:1024
>     [===================>] sync'ed:100.0% (1024/39936)K
>     finish: 0:00:00 speed: 5,556 (5,556) want: 1,024 K/sec

Do I understand correctly that all you are complaining that the *reported*
average resync speed is faster than the configured maximum?

Is this also the case for larger resyncs (full syncs)?
Is this also the case if the device is idle, application wise?

Do you experience performance degradation for your application?

Are you aware that, with DRBD Protocol C, an application write
do a no-in-sync block will also bring this block in-sync,
and thus count to the resync rate -- which "measures" how many
blocks per unit time change from "not-in-sync" to "in-sync"?


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