geom - help ...

[Pawel Jakub Dawidek]

On Fri, Sep 22, 2006 at 08:39:00AM -0500, Rick C. Petty wrote:
> I wouldn't say it's at all better, although it was easier to setup just a
> mirror.  Vinum is a volume manager, so I expect it to be more complex than
> just setting up a mirror.  But I certainly wouldn't call it better.  My
> mirror rebuilds *every* power outtage (and sometimes even at expected
> shutdowns), a behavior I have not witnessed with gvinum.

If gvinum doesn't rebuild mirrors after power failures when the device
is open for writting, then it is a bug in gvinum.

A reliable RAID system has to do it. Imagine a simple situation when
write request is only stored on one component and a power failure
prevents it to be stored on the rest of components. How can you be sure
that the data is in a consistent state?

There should be no rebuilds after clean shutdowns, if there are, please
give me the details, because this is the first time I hear about it.

For gmirror, even if device is open for write, one can define idle time
after which device will be marked as clean. So after few seconds without
writes, even on power failure no rebuild is needed.

I've a code in perforce to avoid rebuilds even after a power failure,
which can be used when gjournal is running on top of gmirror. For such
configuration it is reliable.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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