[Drbd-dev] switching between protocols A and C

[Cristian Zamfir]

Lars Ellenberg wrote:
> On Wed, Apr 11, 2007 at 01:13:32PM +0100, Cristian Zamfir wrote:
>> Hi,
>>
>> Would it be possible to switch from protocol A to C and vice versa 
>> without disconnecting (for instance detach, switch protocol and re-attach)?
>>
>> This would be useful when alternating between two primaries (only 
>> protocol C can be used) and a primary/secondary configuration where 
>> protocol A may increase write throughput on the primary node.
> 
> protocol A does _NOT_ increase throughput at all.
> it _MAY_ reduce latency somewhat sometimes.

I am testing with the bonnie++ benchmark over a 100Mbps link and I get a 
substantial increase for output in the case of protocol A at the expense 
of higher CPU ratio. From what I understand, it would make sense to get 
better throughput from the asynchronous protocol over low quality links. 
Or am I doing something wrong?



drbd connected protocol C

Version  1.03       ------Sequential Output------ --Sequential Input- 
--Random-
                     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP 
/sec %CP
raoul          464M 12764  52 13525   4  8401   0 18724  39 27174   0 
198.4   0
                     ------Sequential Create------ --------Random 
Create--------
                     -Create-- --Read--- -Delete-- -Create-- --Read--- 
-Delete--
               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP 
/sec %CP
                  16 27245  94 +++++ +++ 27305  99 26368  98 +++++ +++ 
22775  95
raoul,464M,12764,52,13525,4,8401,0,18724,39,27174,0,198.4,0,16,27245,94,+++++,+++,27305,99,26368,98,+++++,+++,22775,95


drbd connected protocol A

Version  1.03       ------Sequential Output------ --Sequential Input- 
--Random-
                     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP 
/sec %CP
raoul          464M 27292  90 33632  10 11140   0 19785  46 28524   0 
218.0   0
                     ------Sequential Create------ --------Random 
Create--------
                     -Create-- --Read--- -Delete-- -Create-- --Read--- 
-Delete--
               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP 
/sec %CP
                  16 27136  97 +++++ +++ 26985 100 26775  98 +++++ +++ 
23972 100
raoul,464M,27292,90,33632,10,11140,0,19785,46,28524,0,218.0,0,16,27136,97,+++++,+++,26985,100,26775,98,+++++,+++,23972,100 


> 
>> Right now this behaviour does not seem to be supported but I am 
>> interested if you consider it could be implemented easily.
> 
> no. and it does not make much sense for me, either.
> 

Cristian