ZFS Re: A specific example of a disk i/o problem

Dieter freebsd at sopwith.solgatos.com
Tue Oct 6 04:15:35 UTC 2009

In message <E316139E-FFCF-432F-8DCE-62B120C38E55 at exscape.org>, Thomas Backman writes:

> I run 8.0-RC1/amd64 with ZFS on an A64 3200+ with 2GB RAM and an old  
> 80GB 7200rpm disk.
> My problem is that I get completely unacceptable latency on console IO  
> (both via SSH and serial console) when the system is performing disk  
> IO. The worst case I've noticed yet was when I tried copying a core  
> dump from a lzjb compressed ZFS file system to a gzip-9 compressed  
> one, to compare the file size/compression ratio. screen(1) took at  
> LEAST ten seconds - probably a bit more - I'm not exaggerating here -  
> to switch to another window, and an "ls" in an empty directory also  
> about 5-10 seconds.

You might find the "RELENG_7 heavy disk = system crawls" thread interesting:

} I didn't actually solve it or do anything.
} I just upgraded to RELENG_8.
} Now it's behaving more like FreeBSD should.
} I can do sequential reads/writes and still
} use kbd/mouse/X11/buildworld and so on.

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