ZFS - abysmal performance with samba since upgrade to 8.2-RELEASE

[Sergey Gavrilov]

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 <paul at 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