[Gluster-users] "remove-brick" command SHOULD migrate data

[William L. Sebok]

On Tue, Feb 15, 2011 at 11:49:06PM -0600, Rahul C S wrote:
> For the last question,
> "remove-brick" command does not migrate data, the data in that brick cannot
> be accessed from the client unlike "replace-brick" which actually migrates
> data from one brick to the another.

I strongly suggest for an enhancement a version of remove-brick that actually
does migrate the data.  This would be *extremely* useful in dealing with a
distributed/replicated filesystem with a computer and/or brick that is dead or
likely to be down for an extended period (I configure bricks to be replicated
between different computers). The remove-brick command on startup
could make an estimate whether the data would fit on the remaining bricks.
If after the migration started it turned out that the data really does not all
fit there would still would not be any loss as long as the last file movement
wasn't completely committed.  The command then could be aborted.

This would be no different in concept and risks (and usefulness) than reducing
the size of a partition with gparted.  I would make the remove-brick command
only remove a brick without migrating it if there were some "force" option in
effect.  I have trouble seeing why one would otherwise want to use the
remove-brick command and throw away the data except in some dire emergency.

Bill Sebok      Computer Software Manager, Univ. of Maryland, Astronomy
	Internet: wls at astro.umd.edu	URL: http://furo.astro.umd.edu/