> If we move to extents, we can start to do nifty stuff: there is a
> 32bit start block number, and a 32bit length field in an extent. That
> length field is WAY over dimensioned. You can grab a few bits there
> for "move to another meta-group". Meta-group being a group of 4G
> blocks.
The plan is to use 64 bits for both keys and locations in the extent
map. The extra bits in the location will let us span over multiple
devices if we want to.
The plan was to use 64 bit block and inode pointers as part of doing the
B-tree directory and extent extensions to ext2/ext3. 32 bits would be
reserved for inode and block number, 16 bits would be reserved as an
index into device/volume table, and 16 bits would be reserved for future
use.
I was not planning on extents to use 32 bit length field, because as you
point out, that is a vast overprovisioning of that field. I was
thinking more like 16 bits, maximum.
- Ted
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