"camcontrol identify ada0" and "diskinfo -v ada0" reporting different cylinders count

[Alexander Best]

On Fri Dec 17 10, Bruce Cran wrote:
> On Fri, 17 Dec 2010 11:55:26 +0000
> Alexander Best <arundel at freebsd.org> wrote:
> 
> > 	484518      	# Cylinders according to firmware.
> > 	16          	# Heads according to firmware.
> > 	63          	# Sectors according to firmware.
> > ...
> > cylinders             16383
> > heads                 16
> > sectors/track         63
> 
> 
> > 
> > ...so how many cylinders does my hdd have?
> 
> It almost certainly doesn't have 8 platters for a start, and neither
> does it have 63 sectors per track. CHS is obsolete - the ATA-7
> specification has marked the fields as obsolete and all disks made in
> the last 10 (maybe even 15?) years have used LBA.
> 
> camcontrol displays what the disk reports via the IDENTIFY command
> (I'm not sure if it's the "current" or default geometry it reports):
> ATA says that disks larger than can be represented using CHS should
> report having 16383 cylinders, which is needed for compatibility with
> BIOSes. diskinfo just appears to take the size of the disk,
> assume 16 heads and 63 sectors per track and put the rest into
> cylinders.

thanks for the explanation.

> 
> There's another set of CHS values, and that's in geom: check for
> "fwheads" and "fwsectors" in "gpart list".

Geom name: ada0
state: OK
fwheads: 16
fwsectors: 63
last: 488395021
first: 34
entries: 128
scheme: GPT

> 
> See
> http://lists.freebsd.org/pipermail/svn-src-head/2010-December/023134.html
> for a (very!) detailed discussion of the various ways of calculating
> CHS values. Unfortunately no decision was reached so it looks like
> we're going to have a mismatch between camcontrol, diskinfo, geom, cam
> and ata for a while yet.

too bad. :( thanks for the link. i'll try to read through the entire thread,
although i'm quite sure that the really techie details are too complicated for
me to comprehend.

> 
> -- 
> Bruce Cran

-- 
a13x