On 30 Mar, Manfred Koizar wrote: > On Mon, 29 Mar 2004 08:50:42 -0800 (PST), markw@osdl.org wrote: >>In this case, I've only done 1 per each combination. I've found the >>results for this test to be reproduceable. > > Pardon? I haven't repeated any runs for each combination, e.g. 1 test with 16kb lvm stripe width and 2kb BLCKSZ, 1 test with 16kb lvm stripe width and 4kb BLCKSZ... >>>> Linux-2.6.3, LVM2 Stripe Width >>>>BLCKSZ >>>>(going down) 16 KB 32 KB 64 KB 128 KB 256 KB 512 KB >>>>2 KB 2617 2656 2652 2664 2667 2642 >>>>4 KB 4393 4486 4577 4557 4511 4448 >>>>8 KB 4337 4423 4471 4576 4111 3642 >>>>16 KB 4412 4495 4532 4536 2985 2312 >>>>32 KB 3705 3784 3886 3925 2936 2362 > >>> Does this mean that you first ran all test with 8 KB, then with 4, 2, 16 >>> and 32 KB BLCKSZ? If so, I suspect that you are measuring the effects >>> of something different. >> >>Yes, that's correct, but why do you suspect that? > > Gut feelings, hard to put into words. Let me try: > > Nobody really knows what the "optimal" BLCKSZ is. Most probably it > depends on the application, OS, hardware, and other factors. 8 KB is > believed to be a good general purpose BLCKSZ. > > I wouldn't be surprised if 8 KB turns out to be suboptimal in one or the > other case (or even in most cases). But if so, I would expect it to be > either too small or too large. > > In your tests, however, there are three configurations where 8 KB is > slower than both 4 KB and 16 KB. Absent any explanation for this > interesting effect, it is easier to mistrust your numbers. > > If you run your tests in the opposite order, on the same hardware, in > the same freshly formatted partitions, and you get the same results, > that would be an argument in favour of their accurancy. > > Maybe we find out that those 1.5% are just noise. I did reformat each partition between tests. :) When I have tested for repeatability in the past I have found results to fluxuate up to 5%, so I would claim the 1.5% to be noise. Mark _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
