[DRBD-user] no-disk-flushes ineffective?

'Lars Ellenberg' lars.ellenberg at linbit.com
Thu Mar 19 09:02:23 CET 2009

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, Mar 19, 2009 at 10:16:57AM +1000, Andrew (Anything) wrote:
> Hi Gordan & Lars
> Thanks for your reply.
> 
> I set drbd's rate to something ridiculous just to ensure it wasn't part of
> the problem.
> The bs=512 count=1000 tests ive been doing only use 5-6mbit
> 
> I guess I wont try no-disk-drain then ;P
> 
> They're 100mbit connected via crossover cable. And cause its vmware they are
> AMD pcnet32 interfaces, which as far as I can tell doesn't support
> coalescing tuning.
> 
> DRBD has no trouble pushing exactly 10MB/sec while syncing or doing large
> files.
> 
> 64 bytes from 192.168.0.40: icmp_seq=7 ttl=64 time=0.462 ms
> 64 bytes from 192.168.0.40: icmp_seq=8 ttl=64 time=0.484 ms
> 64 bytes from 192.168.0.40: icmp_seq=9 ttl=64 time=0.467 ms 
> Rtt isn't fantastic in this 2 x vmware sample, didn't know it was this bad
> actually. But, definitely better than 2ms.

well.
that has been a rough guess only.

do a flood ping with large packets.
ping -w5 -f -s 5000

and see what that gives.

> Ill see what I can do about setting up a 2 x gige systems I can put linux on
> natively to test with.
> I had hoped I could just see the result of no-disk-flushes straight away,
> evaluate it, and put it on our live servers, seems nothing can go the easy
> way for me.

;)

> Do you think this 0.400 ms latency is the reason why I see no change
> when I use the no-disk-flushes options?

most likely it hides any such effect.

-- 
: Lars Ellenberg                
: LINBIT HA-Solutions GmbH
: DRBD®/HA support and consulting    http://www.linbit.com

DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.
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