[CentOS] DRBD very slow....

Wed Jul 22 09:59:02 UTC 2009
Coert Waagmeester <lgroups at waagmeester.co.za>

On Wed, 2009-07-22 at 11:16 +0200, Coert Waagmeester wrote:
> Hello all,
> 
> we have a new setup with xen on centos5.3
> 
> I run drbd from lvm volumes to mirror data between the two servers.
> 
> both servers are 1U nec rack mounts with 8GB RAM, 2x mirrored 1TB
> seagate satas.
> 
> The one is a dual core xeon, and the other a quad-core xeon.
> 
> I have a gigabit crossover link between the two with an MTU of 9000 on
> each end.
> 
> I currently have 6 drbds mirroring across that link.
> 
> The highest speed I can get through that link with drbd is 11 MB/sec
> (megabytes)
> 
> But if I copy a 1 gig file over that link I get 110 MB/sec.
> 
> Why is DRBD so slow? 
> 
> I am not using drbd encryption because of the back to back link.
> Here is a part of my drbd config:
> 
> # cat /etc/drbd.conf
> global {
>   usage-count yes;
> }
> common {
>   protocol C;
>   syncer { rate 80M; }
>   net {
>     allow-two-primaries;
>   }
> }
> resource xenotrs {
>   device    /dev/drbd6;
>   disk      /dev/vg0/xenotrs;
>   meta-disk internal;
> 
>   on baldur.somedomain.local {
>     address   10.99.99.1:7793;
>   }
>   on thor.somedomain.local {
>     address   10.99.99.2:7793;
>   }
> }
> 
> 
> Kind regards,
> Coert
> 
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I am reading up on this on the internet as well, but all the tcp
settings and disk settings make me slightly nervous...