AW: [DRBD-user] Re: strange performance problems with drbd

mhaverkamp at kcp.com mhaverkamp at kcp.com
Mon May 8 16:29:10 CEST 2006

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


Software RAID5 is the death of performance.  It is very possible that the 
metadata writes that drbd does will kill performance on a software RAID5. 
I don't know why kernel version would make a difference in this though.

I had major performance issues with RAID5 and drbd also.  Moving to 
hardware RAID5 with a write cache resolved the issue.

Michael Haverkamp



<torsten.neumann at dlh.de> 
Sent by: drbd-user-bounces at linbit.com
05/08/2006 02:56 AM

To
<francis_m at proware.com.tw>, <drbd-user at linbit.com>
cc

Subject
AW: [DRBD-user] Re: strange performance problems with drbd






Hello, I try to find that out.

When I do dd on the raw devices (without drbd) I get speeds from approx. 
40MB/sec. Not very fast but acceptable for the application.
When I do tcpspray to test the network I get 80 till 100 MB/sec also okay.
With drbd I get with recent kernels only 3 (three) MB/sec
Just when the secondary side runs 2.6.5 its 10 times faster with drbd.
I am pretty helpless what more to test. Each subsystem alone works okay. 
Just not together and I see no reason why. So I am looking for a why how 
to track the problem down.

My test results gets even more confusing when I break the hardware raid5. 
When building a drbd device with each single disk the speed is fine. When 
putting linux software raid5 on top it goes unusable slow.
 
Regards
  Torsten 

-----Ursprüngliche Nachricht-----
Von: Francis I. Malolot [mailto:francis_m at proware.com.tw] 
Gesendet: Montag, 8. Mai 2006 09:38
An: drbd-user at lists.linbit.com; NEUMANN, TORSTEN
Betreff: Re: [DRBD-user] Re: strange performance problems with drbd

>the cisco switches between the two hosts don't allow that. Is it worth 
the
>trouble with the network admins or does it explain the very slow drbd
>performance with recent kernel versions?

Try to crossover the link between the two host and do 
$ ifconfig eth0 MTU 6000 


>The trouble is that I don't see any error messages. With other similiar 
drbd
>setups ( drbd 0.7.17 SVN Revision: 2125M and kernel 2.6.16.11 ) on 
different
>hosts I don't see that kind problems. There I got with the same network 
setup a
>speed of approx. 80MB/sec when writing data with dd to the disk.

Please check where's the bottleneck (scsi devices,etc)
Kernel version should not be a problem with this. 


thanks,
francism
FingerPrint:3082 0CB4 0609 2A86 4886 F70D 0107 02A0
----- Original Message ----- 
From: "Torsten Neumann" <torsten.neumann at dlh.de>
To: <drbd-user at lists.linbit.com>
Sent: Monday, May 08, 2006 3:28 PM
Subject: [DRBD-user] Re: strange performance problems with drbd


Francis I. Malolot <francis_m at ...> writes:

> 
> please increase your MTU and feel the power of DRBD.
> here we can pump at 125MB....
>

the cisco switches between the two hosts don't allow that. Is it worth the
trouble with the network admins or does it explain the very slow drbd
performance with recent kernel versions?
The trouble is that I don't see any error messages. With other similiar 
drbd
setups ( drbd 0.7.17 SVN Revision: 2125M and kernel 2.6.16.11 ) on 
different
hosts I don't see that kind problems. There I got with the same network 
setup a
speed of approx. 80MB/sec when writing data with dd to the disk.

Regards,
  Torsten
 
> thanks,
> francism


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