Date: Wed, 9 Feb 2005 16:43:05 -0800 From: "Loren M. Lang" <lorenl@alzatex.com> To: freebsd-geom@freebsd.org Subject: Understanding GEOM Ranking System Message-ID: <20050210004305.GA20199@alzatex.com>
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I'm slightly confused on the ranking system use in GEOM as described in
the geom(4) manpage. The wording of the description seems a little
confusing, but the way I understand it is that any geom instance which
has no consumers attached to anything like a disk or acd geom has a rank
of 1. Any geom that does have some of it's consumers attached to a
provider has a rank of the highest ranked geom providing a service to
this geom. For example, a ufs filesystem is running on a raid1
configuration between partition d on slice 1 on disk ad0 mirrored with
slice 2 on disk ad1 (no disklabel on second disk). This makes two disk
geoms for ad0 and ad1 both with rank 1. Each disk geom has a mbr geom
on top of them with rank 2 (max(1)+1). The bsd geom on slice 1 of disk
ad0 has rank 3 (max(2)+1). The mirror geom on top of the bsd geom and
the mbr geom on disk ad1 has a rank of 4 since max(2, 3)+1 = 4. Then a
dev geom on top of the mirror geom has a rank of 5 (max(4)+1). That dev
geom is what is mounted as a filesystem on freebsd. Is this correct?
dev(5) ---> mirror(4) ---> bsd(3) ---> mbr(2) ---> dev(1) ---> ad0
\-------------> mbr(2) ---> dev(1) ---> ad1
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