2011/5/31 djlee064 <djlee064@xxxxxxxxx>: > From my (bad) memory, I've tried fsync, and the resulting was still > the same in the end, i.e., write 100gb+ and all will be the same. > Can't test it now as it is already running other tasks.. > > I think the small bs (4-8k) results to ~ KB/s level using fsync. and > large, 4m+ will get much higher, but at this large bs, eventually, > results to the same as no-fsync when you continuously write stretch to > 100gb+ > Is this too obvious for anyone? (other than the shortstrkoing effect > which should be at most 20% diff) Caching effect decreases as the writing size increases. Sure, when you write 100GB+ data, the difference may be subtle. (It still depends on your RAM size.) > > how then journal-size (e.g., 1gb, 2gb, etc) set by the ceph actually > effect in performance (other than reliability and latency, etc) > If no reliability is ever needed and, say journal is turned off, how's > the performance effect? from my bad memory again, no-journal worsens > performance or had no effect . But I think this is again, tested 'not > long-enough' > e.g., other than journal flushing to disk (which shouldn't be a major > bottleneck, as Collin said Âstuffs in journal gets continuously > flushing out to disk. > > so in other words, set journal to 10gb, and dd for just 10gb, i should > get an unbelievable performance, then just change dd to 100gb, how > much drop? I haven't try this, > but from my very long test wrtites/read, testing many ranges up to 5TB > actual content, the disk does about 12.5MB/s at most. For small sets, > yes there I see high performance, etc. I am not sure what you mean here. Perhaps somebody can answer it. Sorry. --Henry -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
