Date: Mon, 20 Sep 2010 15:56:41 -0500 From: Jamie Ostrowski <jamie.ostrowski@gmail.com> To: freebsd-fs@FreeBSD.org Subject: understanding block distribution in UFS2 filesystems Message-ID: <AANLkTikmjnW=Man9vLsC0konGp1WiAhc5%2BCiz07UGN7M@mail.gmail.com>
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I thought I understood how block distribution in UFS2 filesystems work,
until I tried running dumpfs on one of my filesystems. The output really
confused me, and the man page doesn't get into detail in explaining the
output. Can anyone explain why I am seeing references to the same "free
blocks" in different cylinder groups?
I thought that the block numbers were unique across the entire
filesystem, but from the output of dumpfs, I see references to free blocks
0-7 in almost every cylinder group.
So are the blocks that are in each cylinder group numbered start over
with a new block 0 in each cylinder group?
In other words, which picture below is true, A, or B:
Cylinder group 0: Uses blocks 0-4000
Cylinder group 1: Uses blocks 4001-8000
Cylinder group 2: Uses blocks 8001-12000
OR -- B:
Cylinder group 0: Uses blocks 0-4000
Cylinder group 1: Uses blocks 0-8000
Cylinder group 2: Uses blocks 0-7000
(IE in that sense blocks must be referenced not only by the block number but
by the cylinder group they are in)
I sure hope so, otherwise I am completely lost on this dumpfs output.
Thanks to anyone who can help clear up some of this confusion.
- Jamie
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