RE: Confused about reshape?

On Sun, 30 May 2010 18:29:16 -0500
"Leslie Rhorer" [off-list ref] wrote:

quoted

	Am I confused about reshaping a RAID5 to RAID6 array, or is there an
error in the man page?  The distro I have on one of my servers - Debian
"Squeeze" - employs mdadm 3.0.3, internally dated Oct. 22, 2009.  The

man

quoted

page that comes with the software specifically says:

-l, --level=

<snip>

	Not yet supported with --grow.

Man page is wrong.  Thanks for reporting.  Fixed in current .git and will
be
in next release.

	Oh, you're welcome.  Thanks to you for all the great work.

The syntax for changing levels is simply:

  mdadm --grow /dev/mdX --level=6

This will preserve the number of data disks.  If you want to change that
(or
anything else) at the same time, you can:

 mdadm --grow /dev/mdX --level=6 --raid-disk=8 --chunk-size=1024 --
layout=left-asymetric

	I'm a little fuzzy on how the number of member disks can be
maintained while adding additional redundancy.  Must the file system(s) be
shrunk so that the total amount of free space on all the members is greater
than the member size?  In my situation, that won't work.  First of all, I am
using XFS, and I don't think XFS will allow shrinking of the file system.
In any case, however, the file system, which fills the entire array which in
turn uses the entire (unpartitioned) space of each member, is over 93% full.
It's an 8 x 1.5T disk RAID5 array with one spare drive.  Or does the --grow
command automatically create a RAID6 array with one missing member?  Should
I remove the spare before issuing the command?  If so, should I add it along
with the command, something like:

mdadm --grow /dev/md0 --level6 --raid-disk=9 --add /dev/sdi

Or will mdadm automagically write the additional information to the 9th
spare / member disk without me doing anything?