When you start talking about dynamically
resizeable filesystems, then you need to change
the kernel FS code, because the active FS needs
to be aware of what changes are going to occur
on the block level, may need to prepare for
these changes and clean up when they are done.
It gets really complicated when you want to
remove a block device from an LVM device. The
LVM device needs to tell the filesystem to
move all data out of logical blocks xxx-yyy,
the filesystem needs to do that, and then
afterwards patch the hole in the LVM address
space by re-addressing nodes and metadata into
the newly shrunken address space. The only
way to avoid this extremely costly re-address
process would be to implement something like
paging block devices into the LVM device (at
least that I can think of right now). That
seems like a lot of trouble to go to just to
get live shrinkable FS's. Live growable FS's
wouldn't be too hard to do with LVMs and a
simple message to the FS code saying that its
block device just grew by X blocks.
Zach Amsden
amsden@andrew.cmu.edu
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