Converting a non-HAST ZFS pool to a HAST pool

[Pete French]

> I'm wondering if I'm missing something here --- because I'm wondering
> if running HAST under ZFS isn't a step backwards.
>
> My quick read of HAST seems to indicate that it's going to manage two
> disks and present them as one disk to ZFS.  The design problem with
> this (especially since we're talking a _lot_ of network (and memory)
> transfers involved) is data corruption --- the idea that ZFS protects
> data better when it can determine one disk has it right while another
> disk has it wrong (as it can when it manages the two disks).
>
> Wouldn't it be better to just have network (iscsi-like) spools
> attached to ZFS?  Individual spools could still fail.  What am I
> missing?  Is there a better description of HAST than the FreeBSD wiki
> page?

I guess in theory the answer there is 'yes' - but have you
actually tried it in practice ? I did this for a while as
an experiment using ggated - the problem is that when
the remote fails (for example) it doesnt signal up to ZFS
properly and instead of ZFS seeing a failed driev it just locks
up. iSCSI had similar issues. Note that this test was a while
ago, and the situation may have improved - but that was the way I
did it at the time I set this up.

Interstingly, I am considering a hybrid - using ZFS as a mirror
over a pair of HAST devices. My servers have hardwar RAID in them
and a pair of drives each, so I could split those, remove the
hardware RAID, and run 4 drives as 2 hast devices with ZFS on top.
That soulds like the best soultuon to me - but you do then
have the issue of doubling your network bandwidth required.

-pete.