HDD slow down in heavy load

[John-Mark Gurney]

k simon wrote this message on Mon, Nov 17, 2014 at 18:17 +0800:
>   I observed sometimes DragonflyBSD do much better than FB in heavy 
> load , eg. squid or zabbix's postgresql database.
>   The difference may related to DFBSD have enhanced CAM DA driver to 
> separate read and write streams, allowing concurrent write completion in 
> the face of many stalled read requests.
>   It's released within DFBSD V2.10 at 2011:
> http://leaf.dragonflybsd.org/mailarchive/commits/2011-04/msg00062.html
> http://leaf.dragonflybsd.org/mailarchive/commits/2011-04/msg00061.html
>   I guess I'm alone for notice it.

Have you verified w/ camcontrol tags that you have no remaining tags
available?  camcontrol tags <dev> -v will inform you of the current
counts...  If you do see dev_active == dev_openinings, then yes, it
might be interested to explore this...

I have a feeling that if your server is so heavily loaded that all
tags are busy, you should probably improve your system w/ more
spindles or better disks or ssds or something of the like...

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."