Yes, I know. But I have a lot of memory and I want it to be used if it improves performance. I tried to test whole system not just fs. And I surprised in why vfs.zfs.prefetch_disable="1" affects so much.
2011/3/18 Paul Mather <p...@gromit.dlib.vt.edu> > > On Mar 18, 2011, at 5:53 AM, Sergey Gavrilov wrote: > > > vfs.zfs.prefetch_disable="1" causes much slow read on sequence data in my > > case. > > > > with vfs.zfs.prefetch_disable="1": > > > > dd if=/pool1/test/idisk1 of=/dev/null bs=1m count=500 > > 524288000 bytes transferred in 18.347177 secs (28575949 bytes/sec) > > > > with vfs.zfs.prefetch_disable="0": > > > > dd if=/pool1/test/idisk1 of=/dev/null bs=1m count=500 > > 524288000 bytes transferred in 3.331806 secs (157358504 bytes/sec) > > > > after few seconds: > > dd if=/pool1/test/idisk1 of=/dev/null bs=1m count=500 > > 524288000 bytes transferred in 0.107767 secs (4865009592 bytes/sec) > > The last dd performance figures are undoubtedly reflecting a read from data > cached in RAM. You should do your test on a file that is bigger than your > RAM size, or at least bigger than the amount of RAM you are dedicating to > ARC. > > Other than that, ZFS prefetching *is* supposed to speed up sequential > accesses, so it's no surprise you notice a speedup in such cases. :-) > > Cheers, > > Paul. > > -- Best regards, Sergey Gavrilov _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
