On 20 maj 2010, at 00.20, Don wrote:

> "You can lose all writes from the last committed transaction (i.e., the
> one before the currently open transaction)."
> 
> And I don't think that bothers me. As long as the array itself doesn't go 
> belly up- then a few seconds of lost transactions are largely irrelevant- all 
> of the QA virtual machines are going to have to be rolled back to their 
> initial states anyway.

Ok - then you are in the dream situation, and your solution could be
free of charge, a one-liner command, and perform better than any
SSD on the market:

Disable the ZIL. You will loose up to 30 seconds of the lastly
written data, and if you use it as a NFS server your clients may
get confused after a crash since the server is not in the state
it should be in. 
You could also turn down the ZFS transaction timeout to loose
less than 30 seconds if you want.
Your pool will always be in a consistent shape on disk (if you
have hardware that behaves).

Remember to NEVER use this pool to anything that actually want
better data persistency, that this is a pool tuned specifically
for a very special case.

In very recent opensolaris there is a zpool property for this,
earlier you had to set a kernel flag when mounting the pool
(and having it unset when mounting other pools, if you want
them to have ZIL enabled).

/ragge

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