[rhelv6-beta-list] Can RHEL6 installer align the disk partition with 4k-sector or raid stripe size?

[Bryan J. Smith]

Many of these issues are a result of manufacturers default disk labels.
They ship a Legacy BIOS/DOS Disk Label (aka "msdos") and default to
using either the 16/63 or 255/63 heads/sectors geometry and/or reserving
the first half-cylinder.  I'm sure Anaconda is just "tip toe'ing around"
to ensure it doesn't squash any existing slices (partitions).

If you want any reason why, revisit the early days of kernel 2.6, parted
and many other components of Anaconda and several other distros that
attempted to implement Extended Int13h Disk Services down to the spec,
where Windows NT 4SP4+ through Windows XP utterly _ignored_ it.  ;)

Truly wiping out any existing disk label is the key to ensuring alignment.
And even then using the "msdos" disk label, I'm not sure the Anaconda
installer is going to do things that might be incompatible if it doesn't
have to.  The only way to force proper alignment is to consider the GPT
partition table, which forces a whole new set of assumptions.

I've been spending a lot of time testing and wrestling with this myself
between NT 5.1, 6.0, 6.1 (XP, Vista, 7, respectively), and newer Linux
distros, and newer drives, just to understand all of the intricate details.
I _know_ Anaconda is taking the "safest" route to preserving the old
compatibilities, per past issues back in the Fedora Core 2 timeframe, when
specs were strictly followed (which Windows utterly ignored).

Just my $0.02 from "outside the box."

--- On Thu, 6/10/10, Pasi Kärkkäinen <pasik at iki.fi> wrote:

> From: Pasi Kärkkäinen <pasik at iki.fi>
> Subject: Re: [rhelv6-beta-list] Can RHEL6 installer align the disk partition with 4k-sector or raid stripe size?
> To: "Red Hat Enterprise Linux 6 (Santiago) Beta releases discussion mailing-list" <rhelv6-beta-list at redhat.com>
> Date: Thursday, June 10, 2010, 2:06 PM
> On Thu, Jun 10, 2010 at 10:29:21AM
> +0800, Kirby Zhou wrote:
> > Are you sure?
> > I think RHEL6 installer does not align partitions.
> > 
> > ~]# parted /dev/sda unit kib print
> > Model: IBM ServeRAID M5014 (scsi)
> > Disk /dev/sda: 291991552kiB
> > Sector size (logical/physical): 512B/512B
> > Partition Table: msdos
> > 
> > Number  Start      End 
>          Size   
>       Type     File
> system  Flags
> >  1      31.5kiB   
> 200812kiB     200781kiB 
>    primary  ext4     
>    boot
> >  2      200813kiB 
> 291989407kiB  291788595kiB  primary   
>            lvm
> > 
> 
> Ok.. I guess RHEL6 then doesn't do it. Any reason why? 
> 
> I know for sure F13 does it. The 2 MB alignment might have
> been wrong,
> I can't check right now, but I think it might have been
> 2048 sectors,
> so that'd make 1 MB (on a drive with 512 bytes/sector).
> 
> "fdisk -u" can be used aswell to check the alignment.
> 
> -- Pasi
> 
> > Regards,
> >    Kirby Zhou    
> >   
> from   SOHU-RD   +86-10-6272-8261