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Re: Raidframe and disk strategy
On Oct 17, 10:55pm, Edgar =?iso-8859-1?B?RnXf?= wrote:
} Subject: Re: Raidframe and disk strategy
} With me, the relevant RAID is not auto-configured, so I can just edit
} But my original question is still open (or I didn't understand that it was
} answered): I can set the component's sorting strategy with dkcntl sdn
} I can set some RAIDframe sorting strategy with dkcntl raidn strategy. But
} seems to be a third sorting strategy: the one I set in the START queue
} Is this really so? If yes, at which point (relative to the two other sorting
} operations) does this sorting take place?
>-- End of excerpt from Edgar =?iso-8859-1?B?RnXf?=
Hello. You're right. I think the pieces ar like this:
1. the dkctl sdn strategy sets the policy by which the system reads
and writes to and from the disk.
2. The dkctl raidn strategy sets the policy by which the system reads
and writes to and from the logical disk, i.e. the raid volume
3. The algorithm indicated in the /etc/raidx.conf queue strategy section
sets the policy by which the raid driver queues requests for the
underlying components of the raid set.
I think, but don't have any hard numbers to back it up yet, that the best
performance is achieved when all the layers are using the same or similar
buffer queueing strategies. I've already shown that I get a 15%
improvement by seting the strategies in 1 and 2 above to be the same.
Just to be redundant, I think the data flow looks something like:
read request from the system to a raid volume.
The system sorts the read request into a list of read requests for the
volume according to the policy specified by dkctl raidn strategy.
Raidframe takes the request from the system and determines which
component(s) contain the data and queues up requests for the disks that
contain the raid set according to the policy set forth in raidx.conf.
The disk drivers for each of the disks that contain the raid set take the
read request from the raid frame driver and sort them into a list of
requests for the disks in question according to the policy set forth by
dkctl sdn strategy.
Hope that helps.
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