Re: Raidframe and disk strategy

[buhrow%lothlorien.nfbcal.org@localhost (Brian Buhrow)]

On Oct 17, 12:03pm, Edgar =?iso-8859-1?B?RnXf?= wrote:
} Subject: Re: Raidframe and disk strategy
} Two more questions on the subject:
} 
} > sets the strategy of raidframe to the default strategy for the system,
} > rather than fcfs.
} How does that play with the usual ``fifo 100'' in the ``START queue'' section?
} 
} > you can easily test various disk sorting strategies
} Where can I find a description/discussion of the different strategies?
} 
} Probably your patch is the cause for our occasional NFS hangs having 
decreased 
} from thirty seconds to a few seconds.
>-- End of excerpt from Edgar =?iso-8859-1?B?RnXf?=


        In answering your question, I find I have a couple for Greg.
Depending on his comments to my notes below, you may have a couple of knobs
you can tweak for performance to the raidframe system to get even more
efficiency out of the system.
        It looks like you can select a number of disk queuing strategies
within raidframe itself, something I didn't realize.  There seem to be  5
choices: fifo, cvscan, sstf, scan and cscan.
Fifo is the one we've been using for years, but the others appear to be
compiled into the system.  Unless my understanding is completely wrong,
cscan is the algorithm which most closely aligns with the priocscan buffer
queue strategy and scan  matches the traditional BSD disksort buffer queue
strategy.  To set a new disk queueing strategy for a given raid set, try
the following:

1.  If the raid set is configured by  startup scripts at boot time, then
edit your raid.conf file for that raid set and change the word "fifo" in
the start queue section to one of the other choices listed above.

2.  Unconfigure the raid and reconfigure it.

3.  If your raid set is configured automatically by the kernel, construct a
raid.conf file that matches the characteristics of your raid set, if you
don't already have one, and change the word "fifo" in the start queue
section to one of the choices listed above.

4.  Turn off autoconfigure with raidctl -A no on the indicated raid set.

5.  Unconfigure and reconfigure the raid set as you did in step 2 above.

6.  Turn on autoconfigure again with raidctl -A yes or raidctl -A root
depending on whether your raid set is a root filesystem or just a raid set
On the system.

        For greg:
Have you played with any of these disk queueing strategies?  Do you know if
they work or, more importantly, if they contain huge disk eating bugs?
Have you done any bench marking to compare their relative performance?

-thanks
-Brian