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From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us>
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To: Daniel Kalchev <daniel@digsys.bg>
Subject: Re: Crazy ZFS ZIL options: md(4) umass(4)
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On Fri, 15 Feb 2013, Daniel Kalchev wrote:

> Some further clarification.
>
> ZIL is only read on crash. If you shut down properly etc, the ZIL 
> will be never read. For most of it's lifetime, the ZIL is write-only 
> safety net. An insurance, if you wish.

Something I did not see mentioned in this discussion thread is that 
the ZIL is only used for synchronous writes.  Database writes and NFS 
writes are usually synchronous writes.  Systems which are not used for 
these purposes might not produce any synchronous writes and so the ZIL 
is not used at all.

As long as the pool disks obey cache sync requests, the integrity of 
the pool is assured.  The integrity of the pool is not dependent on 
data in the ZIL.

Bob
-- 
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/