Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
>
> It has been observed that when protocol A and B is used, there is
>some impact on the I/O performance (especially on sequential writes)
>compared to protocol C. But theoretically, protocols A and B should be faster than C. Why Tiobench results (http://www.drbd.org/performance .html) says that protocol C is good ?
>
> Even i carried out performance tests (using Tiobench tool) on 8.0.3 build and i observed that the results are almost same as the one mentioned on the DRBD site.
>
> Please let me know the reason behind it.
>
LARS REPLY:
>
>because those results are horribly out of date?
>note, kernel 2.4 and DRBD-0.6.6 were used for these tests.
>protocol A and B implementation was broken then.
>
>because there are two aspects to protocol choice in DRBD?
> * latency
> * data safety
>
>because you measured throughput,
>and the choice of DRBD protocol has no impact on sustainable throughput?
>
>we realy should take that page offline.
>or better yet, replace with some more recent benchmarks.
>I'll try to dig some up.
>
>with recent 8.0 resp. 8.2,
>the protocols finally are implemented correct,
>and indeed show the expected latency improvements:
>A exposes nearly local latency,
>B has some latency overhead (order of round-trip-time),
>C latency overhead is (order of round-trip-time plus some).
>
>as mentioned, you trade data safety against latency.
>
>--
>: Lars Ellenberg http://www.linbit.com :
>: DRBD/HA support and consulting sales at linbit.com :
>: LINBIT Information Technologies GmbH Tel +43-1-8178292-0 :
>: Vivenotgasse 48, A-1120 Vienna/Europe Fax +43-1-8178292-82 :
>__
I have carried out performance test on 8.0.3 version using Tiobench
tool. But, results says that Avg latency in case of protocol C is
less compared to protocol A and B (during write operation),
theoretically which is not expected.
Can someone please tell me the reason for it? (refer results given below for Sequential and Random writes)
File size= 1024 DRBD partition size=2GB
Block size= 4096 RAM=256MB
Number of threads =8 RTT=~0.3ms
Random writes:
---------------------------------------------------------------
Rate Max Avg Max CPU
CPU % latency latency Efficiency
---------------------------------------------------------------
2.6.18-53.el5 2.40 20.60 2.616 1426.08 12
(without DRBD)
2.6.18-53.el5
(protocol A) 1.05 11.15 4.206 1503.61 9
2.6.18-53.el5
(protocol B) 1.11 12.53 5.024 1705.55 9
2.6.18-53.el5
(protocol C) 0.99 10.09 1.834 1853.46 10
---------------------------------------------------------------
Sequential writes:
---------------------------------------------------------------
Rate Max Avg Max CPU
CPU % latency latency Efficiency
---------------------------------------------------------------
2.6.18-53.el5 37.85 307.7 0.600 2511.88 12
(without DRBD)
2.6.18-53.el5
(protocol A) 11.37 77.77 1.938 14701.06 15
2.6.18-53.el5
(protocol B) 9.52 62.69 2.240 21407.66 15
2.6.18-53.el5
(protocol C) 12.16 100.6 2.131 15969.09 12
---------------------------------------------------------------
Refer to the attachment for results if the above table is
jumbled up.
Regards,
Azeez
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File size= 1024 DRBD partition size=2GB
Block size= 4096 RAM=256MB
Number of threads =8 RTT=~0.3ms
Random writes:
---------------------------------------------------------------
Rate Max Avg Max CPU
CPU % latency latency Efficiency
---------------------------------------------------------------
2.6.18-53.el5 2.40 20.60 2.616 1426.08 12
(without DRBD)
2.6.18-53.el5
(protocol A) 1.05 11.15 4.206 1503.61 9
2.6.18-53.el5
(protocol B) 1.11 12.53 5.024 1705.55 9
2.6.18-53.el5
(protocol C) 0.99 10.09 1.834 1853.46 10
---------------------------------------------------------------
Sequential writes:
---------------------------------------------------------------
Rate Max Avg Max CPU
CPU % latency latency Efficiency
---------------------------------------------------------------
2.6.18-53.el5 37.85 307.7 0.600 2511.88 12
(without DRBD)
2.6.18-53.el5
(protocol A) 11.37 77.77 1.938 14701.06 15
2.6.18-53.el5
(protocol B) 9.52 62.69 2.240 21407.66 15
2.6.18-53.el5
(protocol C) 12.16 100.6 2.131 15969.09 12
---------------------------------------------------------------