On Sat, 29 Jul 2000, Charles Curley wrote:
> On Sat, Jul 29, 2000 at 02:55:44PM -0700, Dave Lers wrote:
> > On Sat, 29 Jul 2000, Charles Curley wrote:
> > > On Sat, Jul 29, 2000 at 11:04:03AM -0700, Dave Lers wrote:
> > > > A simple
> > > >
> > > > dd if=/dev/hda of=/dev/hdc
> > > >
> > > > works great, super backup method, all you need to do is swap drives
> > > > (plug hdc in where hda was). You want both drives as master, 1 per
> > > > channel. The drive you are writing to needs to be the same size or
> > > > bigger. Since my drives are almost identical I haven't played with,
> > > > don't know how to, utilize extra space if copying to a noticeably
> > > > larger drive.
> > >
> > > This assumes that the two drives have identical sectors per track and
> > > tracks per cylinder. Otherwise the drive geometry won't match the values
> > > in the MBR's partition table. If the new drive has larger values, you are
> > > OK, but you waste a lot of space. If the new drive has samller values, you
> > > are hosed.
> >
> > I don't know anything about drive geometry, are you saying there is
> > more to it than making sure the copied to HD is >= in size? How much
> > wasted space are we talking about? Are you talking about the
> > leftover at end of the disk?, which I assumed could be formated as
> > another partition.
> There are three elements of a hard drive's geometry: number of sectors per
> track, number of tracks per cylinder, and total number of cylinders. I'll
> ignore the sector size as almost all hard drives leave the factory
> formatted with 512 byte sectors.
The only way I can make sense of this is to use real numbers. What I
see in bios is cylinders, head, landz, sector and mode. It seems
all my drives (1-10GB) have head-255, sector-63 when mode-LBA, every
other setting is unique (though pretty close on the mirrored drives).
Is that 63 sectors per track, 255 tracks per cylinder?
...Ok I've been playing around w/ this. What I did was a reverse copy,
old backup/larger disk -> new backup/original/smaller disk.
I was 1 record short on the dd (out of space). The system passed
fsck and seems to be fine. My guess is that that last record has
something to do with that bit of unused space (bigger drive) that
couldn't be copied over. What are the "records", there were aprox.
8448k copied?
...Hmm, just playing with numbers
8958 landz (bios) - 8448k records (dd) = 510
The difference in the drives is 2 cyls
2 cyls x 255 head (bios) = 510
I don't know if that's coincidence or if a definition of terms will
put all the pieces together.
One other thing. According to diskdrake the empty portion of the
larger disk is 15megs while the difference in disk size, according to
bios, is 17megs.
