ZFS RaidZ2 with 24 drives?

[James R. Van Artsdalen]

Thomas Burgess wrote:
> One thing most people don't know about hard drives in general is that
> sometimes up to 30% of the space is actually ECC.  With software raid
> systems like ZFS, this will eventually be somethign that we can take
> advantage of. 

ECC is less than 10% of the space.  The inter-sector gap and gap between
a sector's address and data fields, etc, are larger and more problematic
as rotation speeds increase.

> Because of this,  you can imagine a scenario where  allowing ZFS to
> use this ECC space as raw storage, while leaving the data corrections
> to ZFS would be ideal.  It's not only a matter of space, it will also
> lead to nice improvements in speed.  (more data can be read/written by
> the head as it passes)

The disk drive industry's solution to this is 4K sector sizes.  See
http://www.anandtech.com/storage/showdoc.aspx?i=3691

Even ZFS would need major changes to use drives without ECC without an
increased hard error rate.  I don't see this happening since no
filesystems exist yet for this environment, and since transitions to new
filesystems are so slow (99.9%+ of systems today are running filesystems
architectures at least two decades old).