RE: >16TB RAID0

I'm not 100% sure, but a quick look at the code suggests that
16TB is the upper limit for normal read/write operations on
a block device like /dev/md0 on a 32bit host.  This is because it uses
the page cache, and that uses 4K pages with a 32bit index, hence
16TB.

	Uh-oh!  I hope this doesn't apply to a 64 bit host running
2.6.26-2-amd64, or is it a limitation of md?  In fairly short order (a year,
maybe), I'm going to need to go beyond 16T employing RAID6 on some number
more than eight 3T drives.  I know a lot can happen in a year, but when it
comes to upgrading code, sometimes a lot doesn't happen, either.

A filesystem using a 16TB device would not be limited in the same way
as it caches individual files, not the whole device (individual files
would still be limited to 16TB).
I think if you access the block device with O_DIRECT you might be
able to bypass the 16TB barrier.  Try hacking the program
to add O_DIRECT to the open mode.

	I'm running XFS, but perhaps I could get the developers to put in a
switch for this, if need be.