/dev/sda is not limited to 20 partitions

[Ralph Corderoy]

https://help.ubuntu.com/10.10/installation-guide/i386/partition-programs.html
says

    Linux limits the partitions per drive to 15 partitions for SCSI
    disks (3 usable primary partitions, 12 logical partitions), and 63
    partitions on an IDE drive (3 usable primary partitions, 60 logical
    partitions). However the normal Ubuntu system provides only 20
    devices for partitions, so you may not install on partitions higher
    than 20 unless you first manually create devices for those
    partitions.

This is misleading since the transition from /dev/hda to /dev/sda as the
latter now enforces a limit of 16 minor devices per drive.

    $ ls -l /dev/sd[ab]
    brw-rw---- 1 root disk 8, 0 2010-12-30 16:28 /dev/sda
    brw-rw---- 1 root disk 8, 16 2011-01-13 16:32 /dev/sdb
    $

0 is the whole drive, 1-4 are the primary partitions, 5-15 are the
logical partitions. So there's now a limit of 15 partitions per drive,
assuming you've used all of the primary partitions.

A friend of a friend found installation failed on creating the three
partitions for /, swap, and /home. The first two succeeded, the third
failed with an error passed on imprecisely as "the 17th partition"
couldn't be created. The guide suggests 20 should be OK.

"oh, wait, I'm evidently misremembering and the /dev/sd* limit is indeed
16. Yes, I suppose that should be documented in the installation
guide." -- Colin Watson, #ubuntu-installer, 2011-01-17 10:21.

[Colin Watson (cjwatson)]

I think it would also be nice to have some vaguely sensible UI when you go over the limit.

[Phillip Susi (psusi)]

Actually, all devices, including scsi disks, now support 256 partitions. They just don't get their dev_t minor number allocated in the traditional sequence when you go over 16 for scsi disks.

[Phillip Susi (psusi)]

There was a bug in libparted that prevented partitions > 16 for working correctly. I have fixed it and added it to my pending merge. I have also updated the installation guide.