Re: [Drbd-dev] switching between protocols A and C

[Cristian Zamfir <zamf@dcs.gla.ac.uk>]

Lars Ellenberg wrote:
> On Wed, Apr 11, 2007 at 02:46:02PM +0100, Cristian Zamfir wrote:
>> 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?
> 
> and your exact bonnie++ command line is:
> 
Bonnie++ is run with the default parameters:
bonnie++ -u zamf -d bonnie/

I have results from ./tiobench, with shows a 2.4x increase in 
performance in favour of protocol A:

/usr/bin/tiotest -t 8 -f 60 -r 500 -b 4096 -d . -T-T

Protocol A
Sequential Writes
                               File  Blk   Num                   Avg 
   Maximum      Lat%     Lat%    CPU
Identifier                    Size  Size  Thr   Rate  (CPU%)  Latency 
  Latency      >2s      >10s    Eff
---------------------------- ------ ----- ---  ------ ------ --------- 
-----------  -------- -------- -----
2.6.18-xenU                   480   4096    1   24.27 11.73%     0.126 
     724.87   0.00000  0.00000   207
2.6.18-xenU                   480   4096    2   20.32 10.07%     0.312 
    1002.72   0.00000  0.00000   202
2.6.18-xenU                   480   4096    4   16.57 7.733%     0.648 
    4505.20   0.00570  0.00000   214
2.6.18-xenU                   480   4096    8   15.96 7.445%     1.107 
    6598.77   0.02279  0.00000   214


Protocol C

Sequential Writes
                               File  Blk   Num                   Avg 
   Maximum      Lat%     Lat%    CPU
Identifier                    Size  Size  Thr   Rate  (CPU%)  Latency 
  Latency      >2s      >10s    Eff
---------------------------- ------ ----- ---  ------ ------ --------- 
-----------  -------- -------- -----
2.6.18-xenU                   480   4096    1   10.46 5.032%     0.301 
    1232.91   0.00000  0.00000   208
2.6.18-xenU                   480   4096    2   10.74 5.032%     0.581 
    1981.85   0.00000  0.00000   213
2.6.18-xenU                   480   4096    4   10.55 5.009%     0.849 
    3782.22   0.01302  0.00000   211
2.6.18-xenU                   480   4096    8   10.32 4.923%     1.841 
    8250.74   0.03581  0.00000   210