Date: Mon, 20 Sep 2010 17:40:52 -0500 From: "Rick C. Petty" <rick-freebsd2009@kiwi-computer.com> To: Jamie Ostrowski <jamie.ostrowski@gmail.com> Cc: freebsd-fs@FreeBSD.org Subject: Re: understanding block distribution in UFS2 filesystems Message-ID: <20100920224052.GA88762@rix.kiwi-computer.com> In-Reply-To: <AANLkTikmjnW=Man9vLsC0konGp1WiAhc5%2BCiz07UGN7M@mail.gmail.com> References: <AANLkTikmjnW=Man9vLsC0konGp1WiAhc5%2BCiz07UGN7M@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, Sep 20, 2010 at 03:56:41PM -0500, Jamie Ostrowski wrote: > 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. I suspect the block numbers (which are actually fragment numbers) are relative to each cylinder group. Blocks 0-7 are free in all cylinder groups except the first one, which is used for bootstrap. > 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 This is correct. Each cylinder group contains its own bitmap of free space, a copy of the super block, and the inodes for that group. -- Rick C. Petty
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20100920224052.GA88762>