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because those results are horribly out of date?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 >--------------------------------------------------------------- > Regards, Azeez -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.linbit.com/pipermail/drbd-user/attachments/20080307/7ad5def9/attachment.htm>