The perfect Sun disklabel?

Disk /dev/sda (Sun disk label): 19 heads, 248 sectors, 7508 cylinders
Units = cylinders of 4712 * 512 bytes
 
   Device Flag    Start       End    Blocks   Id  System
/dev/sda1  u          0      7508  17688848    5  Whole disk
/dev/sda2             1        29     65968   83  Linux native
/dev/sda3  u          0      7508  17688848    5  Whole disk
/dev/sda4            30        58     65968   82  Linux swap
/dev/sda5            59      7508  17549844   83  Linux native

Explanation:

1. The first partition needs to start at cylinder 0. This is required for OpenBoot automatic booting. (You could otherwise boot by specifying a partition, e.g. boot disk0:c.) The /boot fs could also start at cyl 0 iff cylinder 0 is never touched (as is the case with ext2 and ufs) -- would not be the case with e.g. xfs. There is no other requirement, so I just made it a dummy partition marked as "Whole disk".

2. The boot sector needs to be ext2, ext3, romfs or ufs, because that's the only thing SILO currently supports. There is no real reason it starts at cylinder 1. (Once upon a time, x86 BIOSes could only read from the first 1024 cylinders. But since this is neither x86 nor an old BIOS, there's no argument.)

3. For compatibility reasons, I heard, the third partition should be "Whole disk".

4. The swap partition, if any, should be at the start (or near the beginning) of the disk because read speeds are higher there.

5. Finally the base filesystem.

Posted 2006-03-30 10:03 / Tags: / link