Date: Thu, 28 Sep 1995 01:09:52 +1000 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, nate@rocky.sri.MT.net Cc: bde@FreeBSD.org, hackers@FreeBSD.org Subject: Re: Diskslice naming convention? Message-ID: <199509271509.BAA28013@godzilla.zeta.org.au>
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>Ok. How do the 'fdisk' slices (of which there can only be 4) relate to >the 30 slices available in FreeBSD. Excuse me for using DOS terminology The `fdisk' slices (primary DOS partitions) are the first 4 of the 30. >for a minute, but if I understand correctly, we can use 'extended' >partitions inside of 'primary' partitions. However, 30/4 isn't a real >number, so where does the magic number 30 come from? Extended partitions aren't inside primary partitions. Each primary partition may be an extended partition. Each extended partition begins with a secondary boot record with a partition table in it. The 4 entries in the partition table may be `logical drives' or extended partitions. Each extended partition begins with a secondary boot record... I decided that 5 bits in the minor number were enough to reserve for the slice number. 2^5 = 32 and 2 slice numbers are special. >> `dd if=/dev/rxd#' reads the entire disk. /dev/rxd# is a completely >> different device from /dev/rxd#c. These devices are often confused >> because disklabel automatically translates from `xd#' to /dev/rxd#c'. >Ahh, so these are equivalent ># dd if=/dev/sd0c of=/dev/null ># dd if=/dev/sd0 of=/dev/null >(Read the entire slice) No, the devices are completely different, as was just explained. >> You can't create a FreeBSD partition which accesses a DOS slice. Just >> access the DOS slice directly. >Ok. How do I know which slice is the DOS slice? (This get's back to >the determination of the numbering scheme 1-30) Look at sysinstall or libdisk/tst01 output for slices labeled as `fat". The numbering corresponds to a particular linearization of the tree of extended partitions so the relative order may vary with the OS. Bruce
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