zfs very poor performance compared to ufs due to lack of cache?

Jeremy Chadwick freebsd at jdc.parodius.com
Wed Sep 15 10:46:38 UTC 2010


On Wed, Sep 15, 2010 at 11:32:18AM +0100, Steven Hartland wrote:
> Ok the results are in, the conclusions I can see from the data, others may see
> more, are:-
> 
> === Common ===
> * arc size on boot is ~180M with a target size of 6.5G
> 
> === sendfile on ===
> * arc size increases on demand but peaks the min value
> * The difference between min and max arc is taken up by inactive pages
> * vm page daemon wakeups sit at a constant level once the machine has
>  filled memory and never fully empties swap.
> 
> === sendfile off ===
> * arc size increases on demand all the way up the the max value
> * vm cache count stays at almost zero all the time
> 
> === conclusion ===
> The interaction of zfs and sendfile is causing large amounts of memory
> to end up in the inactive pool and only the use of a hard min arc limit is
> ensuring that zfs forces the vm to release said memory so that it can be
> used by zfs arc.
> 
> The source data, xls's and exported graphs can be found here:-
> http://www.multiplaygameservers.com/dropzone/zfs-sendfile-results.zip

Looks like Andriy just committed something to HEAD/CURRENT which might
address this:
http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/141305

Commit:

 Author: avg
 Date: Wed Sep 15 10:31:27 2010
 New Revision: 212650
 URL: http://svn.freebsd.org/changeset/base/212650

-- 
| Jeremy Chadwick                                   jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |



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