[CentOS] Stripe vs Cylinder alignement...

Robert Heller heller at deepsoft.com
Fri Oct 30 21:27:09 UTC 2009


At Fri, 30 Oct 2009 11:14:54 -0500 CentOS mailing list <centos at centos.org> wrote:

> 
> 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.

Cylinders only ever existed (as a *physicly mapped* thing) with MFM,
RLL, and early IDE hard drives (IDE drives grew out of 'hard cards',
which were MFM/RLL drives bolted to a XT (pre/early ISA) expansion card
with a MFM/RLL drive controller). (And yes, floppies. Not sure about
CD/DVD-ROMS, but that is a completely different can of worms.)  SCSI
disks *never* had any physical mapping for cylinders, heads, OR
sectors.  The SCSI command protocol uses LBA addressing and has from
day one.  At this point, CHS addressing is pretty much a BIOS 'fantasy'
for any modern disks.

> 
> 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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> > CentOS at centos.org
> > http://lists.centos.org/mailman/listinfo/centos
> >   
> 
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>                  

-- 
Robert Heller             -- 978-544-6933
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