[DRBD-user] performance issues with DRBD :(

Igor Neves igor at 3gnt.net
Wed Dec 16 17:40:35 CET 2009


Hi,


On 12/11/2009 11:19 AM, Mark Watts wrote:
> On Thu, 2009-12-10 at 16:58 +0100, Florian Haas wrote:
>    
>> Lars beat me to this but anyway...
>>
>> On 2009-12-10 13:23, Beck Ingmar wrote:
>>      
>>> Hi Florian,
>>>
>>> why improves bonding of the replication-connection not the performance.
>>>        
>> I did not say that. :) I said round-robin bonding _over 4 NICs_ would be
>> detrimental to performance.
>>
>>      
>>> We currently have a direct connection for the 1 Gb DRBD replication and
>>> I
>>> wanted to activate an active-active bonding (with a further LAN-port). I
>>> would expect nearly double of replication-performance.
>>>        
>> All of the following applies to DRBD Connected in protocol C:
>>
>> - With 1 GBit Ethernet link, you can do about 110 MB/s (provided your
>> storage subsystem has that bandwidth);
>>
>> - With 2 GBit links bonded in round-robin mode, you top out at around
>> 160-170 MB/s (even then you may have to tune kernel TCP parameters);
>>
>> - with 3 Gbit links, your throughput will drop down to around 110 MB/s;
>>
>> - with 4 links or more, you will get _significantly less_ throughput
>> than a single unbonded link.
>>
>> Reason for all this: TCP reordering.
>>
>>      
>>> Or depends it on whether the connection between the nodes directly or
>>> via 1-n switches.
>>>        
>> I am talking about back-to-back connections. Switches could make it worse.
>>
>>      
> Do Jumbo Frames make any difference here?
>    


Yes they help, in both cases (with switch and in b2b scenario). Please 
test everything and put everything working without jumbo frames. Use 
jumbo frames only if you need extra performance and after you have 
everything working.

But there are some other settings, search in google for "linux kernel 
tcp optimizations".


> Mark.
>
>    
>
>
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> drbd-user at lists.linbit.com
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>    

-- 
Igor Neves<igor.neves at 3gnt.net>
3GNTW - Tecnologias de Informação, Lda

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