Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Tue, Dec 09, 2008 at 01:44:37PM +0100, Robert wrote: > Hello list, > > I'm using DRBD 8.2.7rc2 and doing some benchmarks. The standby machine > uses a ramdisk as backend storage to simulate the impact of the network > only. > > I also set up different iometer bechmark patterns. For two of them I can > not explain the results. > > Pattern1: 100% Write, Blocksize 8k, 100% Random > Pattern2: 100% Write, Blocksize 8k, 100% Sequencial > > The network between the sites is 100Mbit with a simulated latency of > 1500 us +- 500 us. > > DRBD (besides std. config) is: > protocol c; > al-extents 1021; > max-buffers 4096; > unplug-watermark 131072; > sndbuf-size 0; > > With the same drbd setup I get : > > Pattern1: 685 IO's /Second > Pattern2: 116 IO's /Second > > I can not explain why sequencial writes are slower than random writes > with the same DRBD config. > > I also tried with different unplug-watermark, no effect. > > Any hint ? watch the network traffic with tcpdump, maybe there is some "interessting" timing behaviour there, congestion control getting in the way or something like that. play with the max-epoch-size (tune it all the way from the minimum to the maximum, and plot the benchmark results) may or may not have any effect. maybe explicitly set a sndbuf-size. see if the behaviour is reproduceable for real backing store. (may be a cpu cache effect, even!) -- : 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 : __ please use the "List-Reply" function of your email client.