Re: cfdisk vs fdisk & speaking of Western Digital drives...

[Andy Firman <andy@firman.us>]

On Sun, Jan 04, 2004 at 12:36:42AM +0100, GCS wrote:
> On Sat, Jan 03, 2004 at 04:52:06PM -0500, Andy Firman <andy@firman.us> wrote:
> > Second, I have 2 Western Digital drives.
> > Both model WD400BB but they were manufactured about
> > 6 months apart.
>  It may be an other revision, hdd controllers can have different
> chipset/'bios'. Also, they may have higher density plates, so less of
> them enough for the same capacity.
> 
> > I partioned both disk's exactly the same using cfdisk 
> > during the install.  It seems that one drive has 4863 cylinders
> > and the other has 77545 cylinders.
>  Can be a BIOS setting, check that both drives use the same addressing
> method (CHS, LBA, other).

Both drives were set as "auto" in the BIOS.

I have learned that LBA = logical block addressing and 
CHS = cylinder head sector.  Not sure of the implications of using either.

Should I try using either and do my partitioning all over again
or should just accept the fact that 2 exact same model WD drives
does NOT mean they are the same physically?
 
> > Why would Western Digital
> > make the drives different?  Or did I do something wrong 
> > with partitioning/formatting?
>  No, partitioning is ok IMHO. What you don't know that hdd size is
> calculated from a triplet: Cylinders, Headers, Sectors:
> >                            Disk Drive: /dev/hda
> >                           Size: 40000000000 bytes
> >            Heads: 255   Sectors per Track: 63   Cylinders: 4863
> >                            Disk Drive: /dev/hdd
> >                           Size: 40020664320 bytes
> >            Heads: 16   Sectors per Track: 63   Cylinders: 77545
> If you do the math: C*H*S*512 => you should get the size in bytes. So
> hdd has more Cylinders because it has less Heads value (this is not the
> real value, but some kind of mapped one).
> 
> > Do the physical drives and partitions have to be EXACTLY the 
> > same for RAID 1 to work properly or will the following
> > layouts of my drives be sufficient?
>  Hmm. Note sure this is ok, try to set the same CHS for both drives.
> 
> > /dev/hda1   *         1       122    979933+  83  Linux
>  Also, if I remember right, a plus sign after the size is indicating a
> warning that the partition does not on Cylinder boundary, which may be a
> problem as partitions may overlap a bit.

I noticed the plus signs but did not know what they indicated.

Maybe the best thing to do is get started with the root on RAID project
and see if these 2 "same model but different" drives cause any grief.

Thanks,
Andy