[CentOS] Using raid 1 for rollback purposes

James Olin Oden james.oden at gmail.com
Fri Oct 19 18:02:55 UTC 2007

Hi All,

For quite some time I've used raid 1 as a means of providing a
rollback mechanism for an upgrade (which I learned from others long
ago).  So essentially, before an upgrade you split the mirrors and
upgrade one side or the other.  If your upgrade goes well you sync one
way, if your upgrade does not you sync the other (much hand waving and
chanting going on, as its more complicated than that, but that is the
essence of the solution).

Recently, I was asked to do the same thing but with a raid 1+0
solution.  Its easy,
enough to break the raid 1 volumes underneath, but then how do I use
the broke off volumes to form the duplicate strip.  Pictures may help.
 We start off looking like:

  /----------- Raid 0 Volume ----------\
  |    [disk 0]<---R 1--->[disk 2]    |
  |                                            |
  |    [disk 1]<---R 1--->[disk 3]    |

What we want to go to is:

  /--- Raid 0 ---\       /--- Raid 0 ---\
  |    [disk 0]   |       |    [disk 2]   |
  |                  |       |                  |
  |    [disk 1]   |       |    [disk 3]   |
  \-----------------/       \------------------/
     Old System       New System

Is this possible with the current set of mdadm tools?


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