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List:       netbsd-tech-kern
Subject:    Re: RAIDframe: stripe unit per reconstruction unit
From:       Greg Oster <oster () cs ! usask ! ca>
Date:       2013-10-18 22:55:38
Message-ID: 20131018165538.70b2d6d8 () quad ! oster ! net
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On Fri, 18 Oct 2013 15:50:55 +0200
Edgar Fuß <ef@math.uni-bonn.de> wrote:

> The man page says:
> 
> The stripe units per parity unit and stripe units per reconstruction
> unit are normally each set to 1.  While certain values above 1 are
> permitted, a discussion of valid values and the consequences of using
> anything other than 1 are outside the scope of this document.
> 
> I noticed that reconstruction seems to read/write in units of one
> stripe unit, which in my case (being 4k) seems rather inefficient. Is
> it possible to accelerate recontruction by using a figure larger than
> 1 here?

If you go here: http://www.pdl.cmu.edu/RAIDframe/
and pull down the "RAIDframe Manual" and go to page 73 of that manual
you will find:

 "When specifying SUsPerRU, set the number to 1 unless you are
 specifically implementing reconstruction under parity declustering; if
 so, you should read through the reconstruction code first."

The answer might be "yes", but I don't know what the other implications
are.  I'd only recommend changing this value on a RAID set you don't
care about, with data you don't care about.  I'd also recommend reading
through the reconstruction code, looking for "SUsPerRU"...

Later...

Greg Oster
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