[CentOS] C7: How to configure raid at install time

Thu Nov 19 18:54:19 UTC 2015
Warren Young <wyml at etr-usa.com>

On Nov 18, 2015, at 9:49 PM, Devin Reade <gdr at gno.org> wrote:
> The one thing I would point out regarding the above link is that despite
> conventional UNIX wisdom, *don't* put /usr on a separate filesystem
> in CentOS 7.  <sarcasm>Thank you RedHat</sarcasm>
> Flames to /dev/null.

Sorry, you don’t get to throw that grenade and then run away.

The old wisdom you refer to is simply obsolete, and it wasn’t Red Hat that made it so.  ’Twas *progress* that made it so, specifically the fact that even a throwaway USB key has enough space to hold the complete OS on it these days.  We no longer live in a world of 5 MB disk packs the size of extra large pizzas.

Several OSes made /usr/{bin,lib} the same as /{bin,lib} way before Red Hat: Solaris, OS X, and Cygwin, at the least.  Probably all of the embedded Linuxes, too.

Even FreeBSD is starting to give up on /usr as separate from /.  Although its installer still lets you put /usr into a separate slice, the boot process will break if you put it onto a different physical disk that the boot kernel can’t see, or use a different filesystem for it that isn’t compiled into the boot kernel.

A truly “traditional” Unix OS wouldn’t have this problem: as long as the tools necessary to mount /usr are in /, it would be able to boot.

If you disbelieve that, try installing FreeBSD 9.0 (i.e. pre-ZFS-boot) into a VM, then move /usr into a ZFS pool.  It won’t even boot into single-user mode!  Ask me how I know.