Hi,

I've been trying to understand how transactional writes work in
RAID-Z.  I think I understand the ZFS system for transactional writes
in general (the only place I could find that info was wikipedia;
someone should fix that!).  For RAID-Z it seems to me that the only
way to make it transactional is to have a single tree of blocks
spanning all disks, so that, e.g., the blocks in a stripe across three
disks will all share a single parent block.  Is that how it works?

Oh, also doesn't the model (non-RAID, even) imply every write
generates at least log(N) writes (the parent node changes because it
stores child pointers, and it propagates up the tree).  I understand
that transaction groups would limit that effect, of course.


Thanks,

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com

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