[Bug 704412] Re: /dev/sda is not limited to 20 partitions

Phillip Susi psusi at ubuntu.com
Fri May 13 01:40:38 UTC 2016

** Branch linked: lp:~psusi/ubuntu/yakkety/installation-guide/partition-

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  /dev/sda is not limited to 20 partitions

Status in installation-guide package in Ubuntu:

Bug description:

      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

  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.

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