gemor mirror and priority

[Clifton Royston]

On Fri, Mar 20, 2009 at 05:39:14PM +0000, Pete French wrote:
> > I'll try it and report after the weekend :)
> 
> It should be OK - we ran it here on the main database server until
> a couple of months ago, which I went back to using vanilla 7.1 in an attempt to
> try and track down a bug. I will probably continue to use the patch in
> future though - it's very stable, and very useful if you haave some
> kind of "homemade clustering" solution with a local and remote drive.

  Even if you don't, I think it's quite useful to make the *default*
priority set when creating a mirror be some value which allows both
higher and lower values to be specified.  I hadn't known about that
issue until I read the original thread here a while back.If the default
were set to some mid-range value, or even to 2, for example, then at
least creating a new mirror and adding drives without setting a
priority would continue to behave as usual, while it would be possible
to explicitly insert new components with a lower priority.  (I see why
one wouldn't want to change the default interpretation of existing
priority values for POLA reasons.)

  There are lots of reasons one could want to control priorities of
mirrored drives in various ways.  One is to use gmirror as a long-term
backup approach: mirror with three drives, periodically disconnecting
one from the mirror to swap it with a fresh drive from a pool of backup
drives.  I haven't tried this, but it's been on my mind to mess around
with soon.

  In this case, I would want the designated backup drive to always be
lowest-priority, to ensure the mirror never accidentally started
rebuilding from a newly reinserted backup.  (This probably wouldn't
happen anyway, but it would be nice to be sure...)
 
  -- Clifton

-- 
    Clifton Royston  --  cliftonr at iandicomputing.com / cliftonr at lava.net
       President  - I and I Computing * http://www.iandicomputing.com/
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