Re: ext4 features (checksums)

[Jeff Garzik <jeff@garzik.org>]

Neil Brown wrote:
> Can't say I agree with this layering distinction.
> It's been some years that I've felt that most 'logical volume
> management' really belongs in the filesystem.
> Why have a dm that chops devices up in to segments and assembles them to
> look like a big device, only to have that big device chopped up and
> presented as files.  Seems like double handling to me.

Agreed, and allow me to take an even more radical position:

I've long felt that things like snapshotting and mirroring made a lot of 
sense at the filesystem level -- as do layered filesystems, just like we 
layer block devices.

Block device drivers (MD, DM) get ever more complicated, and ultimately 
become mini-filesystems themselves.  The metadata managed by blkdev 
drivers continues to increase in complexity.  What is represented to the 
upper layer as a contiguous run of bytes is really, under the hood, 
chunks of data coalesced logically -- just like files in a filesystem.

The more complex that blkdev drivers become, the more and more they will 
look like filesystems.

	Jeff