[CentOS] DRBD very slow....

Mon Jul 27 22:18:07 UTC 2009
Ross Walker <rswwalker at gmail.com>

On Jul 27, 2009, at 4:09 PM, Coert Waagmeester <lgroups at waagmeester.co.za 
 > wrote:

>
> On Mon, 2009-07-27 at 12:37 +0200, Coert Waagmeester wrote:
>> On Mon, 2009-07-27 at 12:02 +0200, Alexander Dalloz wrote:
>>>>
>>>> On Mon, 2009-07-27 at 08:30 +0200, Coert Waagmeester wrote:
>>>
>>>>> Hello Roman,
>>>>>
>>>>> I am running drbd 8.2.6 (the standard centos version)
>>>
>>>
>>> have you considered to test the drbd-8.3 packages?
>>>
>>> http://bugs.centos.org/view.php?id=3598
>>>
>>> http://dev.centos.org/centos/5/testing/{i386,x86_64}/RPMS/
>>>
>>
>> Thank you very much for this tip! It was one very obvious place  
>> where I
>> did not look yet.
>>
>>
>> Would it be necessary to still recompile it for the TCP_NODELAY and
>> such?
>>
>> I am just making sure, because
>> http://www.nabble.com/Huge-latency-issue-with-8.2.6-td18947965.html
>> makes it seem unnecessary.
>>
>> Why do the repositories provide both DRBD 8.0.x and 8.2.6?
>>
>
> Here is a status update....
> _______________________________________________________________________________
 

> on both hosts I now run from the testing repository:
> # rpm -qa | grep drbd
> drbd83-8.3.1-5.el5.centos
> kmod-drbd83-xen-8.3.1-4.el5.centos
> _______________________________________________________________________________
 

> Here is my config (slightly condensed):
> -----------------------------------------------------
> global {
>  usage-count yes;
> }
> common {
>  protocol C;
>  syncer { rate 50M; }
>  net {
> #        allow-two-primaries; }
>         sndbuf-size 0; }
> #  disk {no-disk-flushes;
> #        no-md-flushes; }
>  startup { wfc-timeout 0 ; }
> }
> resource xenfilesrv {
>  device    /dev/drbd1;
>  disk      /dev/vg0/xenfilesrv;
>  meta-disk internal;
>
>  on baldur.mydomain.local {
>    address   10.99.99.1:7788;
>  }
>  on thor.mydomain.local {
>    address   10.99.99.2:7788;
>  }
> }
> resource xenfilesrvdata {
>  device    /dev/drbd2;
>  disk      /dev/vg0/xenfilesrvdata;
>  meta-disk internal;
>
>  on baldur.mydomain.local {
>    address   10.99.99.1:7789;
>  }
>  on thor.mydomain.local {
>    address   10.99.99.2:7789;
>  }
> }
> _______________________________________________________________________________
 

>
> xenfilesrv is a xen domU
> in this domU i ran a dd with oflag direct:
> ---------------------------------------------------------
> # dd if=/dev/zero of=1gig.file bs=1M count=1000 oflag=direct
> 1000+0 records in
> 1000+0 records out
> 1048576000 bytes (1.0 GB) copied, 147.997 seconds, 7.1 MB/s
>
> Just before I ran the dd this popped up in the secondary hosts syslog:
> ----------------------------------------------------------------------
> Jul 27 21:51:42 thor kernel: drbd2: Method to ensure write ordering:
> flush
> Jul 27 21:51:42 thor kernel: drbd1: Method to ensure write ordering:
> flush
>
>
> _______________________________________________________________________________
 

>
> What more can I try?
>
> To be quite honest, I have no idea what to do with/ where to find the
> TCP_NODELAY socket options......

Use drbd option to disable flush/sync, but understand that during a  
power failure or system crash data will not be consistent on disk and  
you will need to sync the storage from the other server.

-Ross


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