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up vote 4 down vote favorite

During some basic RHEL training, I came across this blurb:

Although it's possible to create more, RHEL will recognize only up to 16 partitions on any individual SATA, SCSI, PATA, or virtual hard drive.

That sentence seems to conflict with itself. If RHEL can't recognize more than 16 partitions, why would I ever want to create more than 16?

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Why the down vote? As per my request on meta, training related questions seem to be appropriate: meta.unix.stackexchange.com/questions/1139/… – Mike B Jan 19 at 22:31
For what it's worse, I can access over 100 partitions on usb storage, scsi disk and ata disk with a 3.5 kernel. With nbd and loop devices at least, the maximum can be set as a parameter to the kernel module. I don't know where that 16 is coming from. The only place where I've found a limitation was on virtio drive, and the limit was 16, not 15. – Stephane Chazelas Jan 21 at 15:39

2 Answers

up vote 6 down vote accepted

There was a bit of discussion about that topic in an old bug report on exactly that limit:

  • They used to reside in different (smaller) disks (and may go back). Several partitions give me more flexibility to move them around using labels.
  • I wasn't using ext3 before, so smaller partitions made shorter fscks in the case of power-downs.
  • I'm too lazy to use quotas to limit dept. disk usage

But even then the short answer was: anyone who needs even 16 partitions is insane, :).

Nowadays we have LVM and those limits do not matter anymore. :)

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So in order words, there isn't a practical and legitimate reason for having more than 16 partitions on a system? – Mike B Jan 19 at 22:40
I cannot think of a good reason. If you really run into that limit, you probably should rethink what you are doing. - There is definitely a better way of doing it. – michas Jan 19 at 22:52
+1'ed for the LVM part of the answer. Nobody cares about more than 3 partitions anymore (swap, /boot and lvm pv) – Dennis Kaarsemaker Jan 19 at 23:11
up vote 1 down vote

The limitation to 15 partitions per disk (yes, it's 15, not 16) is in Linux's generic SCSI driver, which is used for most hardware connection types these days (IDE, SATA, SCSI, USB, Firewire, …).

You can still create as many partitions as you like, but Linux won't be able to access them. Other operating systems might be able to access them.

I think there's a patch floating around to increase the limit. As it gets difficult to manage many PC-style partitions, most systems with many partitions use LVM nowadays. And while dual-boot systems require more partitions, those have become rare now that virtual machines are commonplace.

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It really is 16 partitions, just that partition 0 is the whole disk. And the limit is deeply ingrained in the device numbering, so I doubt it is easy to change (haven't looked at that stuff in a long time). – vonbrand Jan 21 at 17:40

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