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List:       evms-devel
Subject:    Re: [Evms-devel] Basic Help
From:       Steve Dobbelstein <steved () us ! ibm ! com>
Date:       2005-05-31 17:33:48
Message-ID: OFE8E1D9BD.42DFA861-ON05257012.005D1F1B-05257012.00607A90 () us ! ibm ! com
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Dirk Heinrichs <ext-dirk.heinrichs@nokia.com> wrote on 05/31/2005 12:41:44
AM:

> Am Dienstag, 31. Mai 2005 04:34 schrieb ext Brett I. Holcomb:
>
> > For example, the docs mention a BBR Feature but the only BBR that shows
> > up on my system is as a Segment manager - why the discrepancy?
>
> Because it used to be a feature in EVMS 1. So it seems the documentation
is
> a bit outdated there.

The BBR Feature and BBR Segment Manager are different plug-ins that
implement bad block relocation but at different places in the volume stack.
The BBR Feature adds the bad block relocation ability on top of any storage
object but only beneath another feature or a volume.  (In the EVMS view,
disks are on the bottom of a volume stack.)  So, for example, you could add
the BBR feature on top of a RAID0 region, but you can't build a RAID0
region from a BBR feature object.  The BBR Segment Manager can only be
applied to disks or segments but can go beneath any segment, region,
feature or volume.  So although you can't build a BBR segment from a RAID0
region you can build a RAID0 region from a BBR segment.

The bad block relocation functionality really only makes sense down at the
disk level.  You want to handle the errors closest to the device that has
them.  Therefore the BBR Feature has been phased out in favor of the BBR
Segment Manager.  EVMS still ships a BBR Feature plug-in to support older
system configurations that may still use it.  The BBR Feature will discover
a BBR feature in a volume stack, but it will not let you create one.

Steve D.



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