Hammer bootloader

Matthew Dillon dillon at apollo.backplane.com
Thu Aug 28 20:39:04 PDT 2008

:Is there any reason not to avoid writing in the first 8K?  Ext2 on
:Linux for example leaves the first 4K free, and I intend to do the
:same, just to leave space for a boot block in case somebody needs it.

    I think there are good arguments to leave significant space at the
    beginning, and also good arguments not to.   The real issue here is
    not so much the filesystem, but the disklabel or partitioner the
    filesystem is sitting in.

    32 bit disklabels specify block numbers in-band and allow filesystems
    to start at block 0, which overlaps the label and boot area.  It is for
    this reason that filesystems have traditionally reserved some space
    at the beginning.  One can still use a filesystem that does not reserve
    space with a 32 bit disklabel, one simply must start the filesystem at
    a higher block number (block 16 is typical, which reserves 8K at the
    beginning of the label).

    GPT and 64 bit disklabels specify block numbers out-of-band and do not
    allow filesystems to start at the real block 0.

					Matthew Dillon 
					<dillon at backplane.com>

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