sfdisk: confused about disk size

sfdisk: confused about disk size

The size of disk in the sfdisk command is based on number of cylinders
(this is probably legacy from CHS epoch). That's wrong because
partitions are addressed in sectors (LBA), so cylinders don't provide
necessary resolution (granularity).

On Sat, Jan 02, 2010 at 01:01:16PM +0100, Giulio wrote:
> $ cat /sys/block/sda/size
> 184549376
>
> $ sfdisk  -d /dev/sda > part.dump
> $ cat part.dump
> # partition table of /dev/sda
> unit: sectors
>
> /dev/sda1 : start=     2048, size=  2097152, Id=83
> /dev/sda2 : start=  2099200, size= 12582912, Id=83
> /dev/sda3 : start= 14682112, size= 84934656, Id=83
> /dev/sda4 : start= 99616768, size= 84932608, Id=83
>
>
> $ sfdisk  -L  /dev/sda < part.dump
> Checking that no-one is using this disk right now ...
> OK
>
> Disk /dev/sda: 11487 cylinders, 255 heads, 63 sectors/track
> Old situation:
> Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0
>
>    Device Boot Start     End   #cyls    #blocks   Id  System
> /dev/sda1          0+    130-    131-   1048576   83  Linux
> /dev/sda2        130+    913-    784-   6291456   83  Linux
> /dev/sda3        913+   6200-   5287-  42467328   83  Linux
> /dev/sda4       6200+  11487-   5287-  42466304   83  Linux
> Warning: given size (84932608) exceeds max allowable size (84921887)

 disk size:

 based on number of cylinders:   11487 * 8225280 = 94483791360 bytes
 based on number of sectors:     184549376 * 512 = 94489280512 bytes

 end of 4th partition (LBA in bytes):
                     (99616768 + 84932608) * 512 = 94489280512

Reported-by: Giulio <giulioo@gmail.com>
Signed-off-by: Karel Zak <kzak@redhat.com>