[conspire] md raid as backup?

[Tony Godshall]

Hi, folks

I've been playing with USB2 drives and md RAID, both in raid1 (n-way
mirroring) and the new raid10 (raid1+raid0 but better: n-way
redundancy spread among m drives).  (Sadly raid10 isn't really
growable, but growable raid5 is available in the bleeding edge
kernel.)

One strange idea has popped into mind- maybe you folks can tell me if
my thinking is
(a) out of the box
...or...
(b) out of the mind

I spend my days in three usual places the office, the home with the
wife and cats, and the home near the office.  Say I have a USB2 (for
low price and hotpluggability) at each place.  And I'm concerned about
laptop hard-drive failure, since I've had two fail in the past year.

Say I set up my notebook to have /home mounted in a RAID1 partition.
When I use my laptop alone it's running with just md in a
all-failed-but-internal mode, which works, and when I sit down at
location X, I plug in an external USB2 drive and mdadm --re-add it,
and it proceeds to use spare I/O cycles to sync any changes I've made
since it saw the laptop last.  When I go, I hibernate the laptop, and
that USB2 drive gets failed until I sit down at location X again.

Essentially I'd run a 4-way mirrornig RAID of which at any given time
two or three would be "failed" and one or two would be active.  And if
my notebook drive ever fails, I have three copies at reasonably recent
states that should automatically negotiate the latest good /home.

Is there anything wrong with this other than it being unconventional?

Tony Godshall (g)