Re: [SLUG] Partition Question

From: Ian C. Blenke (icblenke@nks.net)
Date: Thu Feb 21 2008 - 16:53:38 EST


Bob Stia wrote:

>Thanks to all who answered. Figured that was so. Reason I asked is that in
>SUSE 10.3 They are loading libata drivers as default. This limits the
>partitions to 15. If I want to load the IDE drivers I have to say so at boot.
>I was wondering if the SATA drive would act the same as the IDE drives. Hence
>my question.
>
>

This isn't a libata thing, this is a sdmod (scsi disk module) thing vs
an ide block device thing.

Look at your /dev/ tree for hda and hdb:

    # ls -la /dev/hda
    brw-rw---- 1 root disk 3, 0 Mar 14 2002 /dev/hda
    # ls -la /dev/hdb
    brw-rw---- 1 root disk 3, 64 Mar 14 2002 /dev/hdb

Notice how the minor number jumps from 0 to 64.

This would allow /dev/hda1 through /dev/hda63, and /dev/hdb1 through
/dev/hdb63, etc.

Now do the same for sda and sdb:

    # ls -la /dev/sda
    brw-rw---- 1 root disk 8, 0 2002-03-14 16:51 /dev/sda
    # ls -la /dev/sdb
    brw-rw---- 1 root disk 8, 16 2002-03-14 16:51 /dev/sdb

Notice how the minor number jumps from 0 to 16.

This effectively means that you _are_ limited to 15 partitions:
/dev/sda1 through /dev/sda15.

This is a holdover from major/minor device assignment decisions made a
long time ago primarily to allow 4 IDE drives with the IDE block device
driver using only one major number, and to allow 15 IDE drives with the
SCSI block device driver using only one major number.

This is not a _partitioning_ limitation, it's a _block device driver_
limitation.

With the advent of dynamic udev device allocation, and the growth of
major numbers beyond an 8bit value, things become a bit more interesting.

As for partitioning: There are many different kinds of partitioning.

MBR partitioning with primary and extended partitions are just the kind
of partitioning you're currently used to.

GPT (GUID Partition Table) is the latest craze for Vista and 2008, but
there are other kinds of partitioning like Solaris partitioning that
exist out there that you might want to be aware of as well.

I hope this helps clear things up.

- Ian C. Blenke <ian@blenke.com>

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