[CentOS] Stripe vs Cylinder alignement...

Blake Hudson blake at ispn.net
Fri Oct 30 17:14:54 UTC 2009


Cylinders are largely logical - even in magnetic disks you have no way 
of knowing if the logical cylinder matches up with the physical 
construct of a cylinder on the disk medium - in any modern(15 years ?) 
disk they won't. Don't worry about cylinders, just align your fs to the 
stripe/sector.

Obviously, the concept of a cylinder starts to go out the window with 
RAID, SSD's, etc.

More information about partition alignment here - 
http://www.ocztechnologyforum.com/forum/showpost.php?p=335049&postcount=134

--Blake

-------- Original Message  --------
Subject: [CentOS] Stripe vs Cylinder alignement...
From: John Doe <jdmls at yahoo.com>
To: centos at centos.org
Date: Friday, October 30, 2009 9:45:59 AM
> Hi,
>
> I modified my kickstart to do some custom partioning and formating in a pre-install script.
> I am trying to align the partitions on the RAID stripe (and format with a correct stride).
> But, sfdisk complains that it does not start/end on a cylinder boundary (used -L option to limit complaining).
> Since the cylinder size is not a multiple of the stripe size, I cannot align on both.
> I tried to align the begining on the stripe and the end on the end of a cylinder, but sfdisk still compains...
> Basicaly, I have a 128KB (256 sectors) stripe, and 255*32 = 8160 sectors cylinders.
> What I am doing is:
> begin = ( begin / 256 ) * 256
> end = ( end / 8160 ) * 8160 -1
> So, for my first partition (96MB):
>   begin=256
>   size = ( ( 96 * 1024 * 2 ) / 8160 ) * 8160 = 195840 sectors
>   end = 195840 - 1 - 256 = 195583
> Any idea what I am doing wrong in my calculations or logic?
>
> Thx,
> JD
>
>
>       
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