Robert Milkowski <[EMAIL PROTECTED]> writes:
> Hello David,
>
> Tuesday, July 11, 2006, 8:34:10 PM, you wrote:
>
> DA> Hi,
>
> DA> I've been trying to understand how transactional writes work in
> DA> RAID-Z. I think I understand the ZFS system for transactional writes
> DA> in general (the only place I could find that info was wikipedia;
> DA> someone should fix that!). For RAID-Z it seems to me that the only
> DA> way to make it transactional is to have a single tree of blocks
> DA> spanning all disks, so that, e.g., the blocks in a stripe across three
> DA> disks will all share a single parent block. Is that how it works?
>
> With RAID-Z one FS block is spread onto N-1 disks + one parity.
> So you have one FS block which is divided to smaller N-1 "device"
> blocks. It's clever "trick" with it's own pros and cons.
It's not unfamiliar to me; that's standard RAID5-ish striping AFAICT.
But you're not answering my question:
How can RAID-Z preserve transactional semantics when a single
FS block write requires writing to multiple physical devices?
--
Dave Abrahams
Boost Consulting
www.boost-consulting.com
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