[DRBD-user] Re: Poor network performance on 0.7.22

Oliver Hookins oliver.hookins at anchor.com.au
Wed Jun 18 04:39:14 CEST 2008


Anybody have any tips at all for this issue? I'm running out of ideas...

On Thu Jun 12, 2008 at 16:04:10 +1000, Oliver Hookins wrote:
>Hi again,
>
>I've been doing a lot of testing and I'm fairly certain I've narrowed down
>my performance issues to the network connection. Previously I was getting
>fairly abysmal performance in even DRBD-disconnected mode but I realise now
>this was mainly due to my test file size far exceeding the al-extents
>setting.
>
>I am performing dd tests (bs=1G, count=8) with syncs on the connected DRBD
>resources and getting about 10MB/s only. The disks are 10krpm 300GB SCSI and
>can easily get sustained speeds of 60-70MB/s when DRBD is disconnected or
>not used. There is a direct cable between the machines giving them full
>gigabit connectivity via their Intel 80003ES2LAN adaptors (running the e1000
>driver version 7.3.20-k2-NAPI that is standard with RHEL4 x86_64). I have tested
>this connection with Netpipe and get up to 940Mbps.
>
>However DRBD still crawls along at 10MB/s. I have attempted to increase the
>/proc/sys/net/core/{r,w}mem_{default,max} settings which were previously all
>at 132KB, to 1MB for defaults and 2MB for max without any increase in
>performance. MTU on the link is set to 9000 bytes.
>
>In drbd.conf I have sndbuf-size 2M; max-buffers 8192; max-epoch-size 8192.
>I've also played a little with the unplug watermark setting it to very low
>and very high values without any apparent change.
>
>Taking a look at a tcpdump of the traffic the only weird things I could see
>are a lot of TCP window size change notifications and some strange packet
>"clumping", but it's not really offering me any insights I can immediately
>see.
>
>Is there anything else I could tune to solve this problem?
>
>-- 
>Regards,
>Oliver Hookins



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