[RndTbl] linux md RAID6 + XFS + add 1 drive

[Trevor Cordes]

On 2014-09-10 Adam Thompson wrote:
> ZFS has three major advantages for most people: 1) no RAID write-hole 
> behaviour; 2) automatic resilvering; 3) integrated, effectively 
> infinite, snapshots with built-in replication.

Hey, I've loved the ZFS idea since the day I heard about it.  Until
now it appeared to be the be-all-end-all kitchen-sink.  Now I find out
it has no +1 capability, it loses its luster a little.

Outside of the enterprise space, I can see lots of scenarios where you
want to add a less-than-double amount of disks to an existing array.
Especially for home use, where you only want to do the big $1500 outlay
on disks every 3-6 years (generally when capacities per $ have
doubled).

If you find yourself in the "shoot, we should have bought 1 more disk"
after your array is full, then having no option but buying another X
drives when your budget is spent kind of sucks.  The ability to solve a
full-array problem by spending just $150 on one disk at any time is very
attractive.

I have a funny feeling that md and the FS's on top of it will slowly
add many ZFS features to be almost as rich as ZFS.  If ZFS has
intentional limitations such as the above, then ZFS will never allow
+1.  Things will balance out in the end.  A month ago I would have told
you that ZFS would have taken over the world eventually.  I for one am
happy it won't, because I love the array/FS choices Linux gives: the
more the merrier.  And those kernel md RAID guys are *really* on the
ball (I read the mailing list).