Questions about RAID 6

["Tim Clewlow" <tim@clewlow.org>]

Hi there,

I'm getting ready to build a RAID 6 with 4 x 2TB drives to start,
but the intention is to add more drives as storage requirements
increase.

My research/googling suggests ext3 supports 16TB volumes if block
size is 4096 bytes, but some sites suggest the 32 bit arch means it
is restricted to 4TB no matter what block size I use. So, does ext3
(and relevent utilities, particularly resize2fs and e2fsck) on 32
bit i386 arch support 16TB volumes?

I intend to use mdadm to build / run the array. If an unrecoverable
read error (bad block that on disk circuitry cant resolve) is
discovered on a disk then how does mdadm handle this? It appears the
possibilities are:
1) the disk gets marked as failed in the array - ext3 does not get
notified of a bad block
2) mdadm uses free space to construct a new stripe (from remaining
raid data) to replace the bad one - ext3 does not get notified of a
bad block
3) mdadm passes the requested data (again reconstructed from
remaining good blocks) up to ext3 and then tells ext3 that all those
blocks (from the single stripe) are now bad, and you deal with it
(ext3 can mark and reallocate storage location if it is told of bad
blocks too).

I would really like to hear it is either 2 or 3 as I would prefer
not to have an entire disk immediately marked bad due to one
unrecoverable read error - I would prefer to be notified instead so
I can still have RAID 6 protecting "most" of the data until the disk
gets replaced.

Regards, Tim.