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List:       netbsd-users
Subject:    Re: Optimal block size for dd
From:       Thor Lancelot Simon <tls () rek ! tjls ! com>
Date:       2003-08-31 16:52:57
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On Sun, Aug 31, 2003 at 05:11:35PM +0100, Michael Blake wrote:
> On Sunday 31 August 2003 9:57 am, Chris Pinnock wrote:
> > On Sat, Aug 30, 2003 at 06:42:53PM +0100, Michael Blake wrote:
> > > I'm trying to make an image of a NTFS partition, and wondered what the
> > > optimal block size is. I've tried 512B, but it seems really slow...
> >
> > IIRC, the optimal size for copying disc partitions is to do it a
> > cylinder at a time.
> 
> 
> Hi Chris
> 
> Fdisk reports two different cylinder sizes, which one is the 'correct' one to 
> use?

You can't actually know the "cylinder" size on modern disks; they don't
expose their actual geometry to the user.  Don't bother trying to guess
it; just pick a nice large size and away you go.

One thing to keep in mind is that dd is synchronous: read a block, write
a block, read a block, write a block... this will limit performance in
many cases.  Something like 'ddd' or 'buffer' will often perform better.

-- 
 Thor Lancelot Simon	                                      tls@rek.tjls.com
   But as he knew no bad language, he had called him all the names of common
 objects that he could think of, and had screamed: "You lamp!  You towel!  You
 plate!" and so on.              --Sigmund Freud
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