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Date: Mon, 19 Jun 2006 12:55:22 -0700 (PDT)
From: "R. B. Riddick" <arne_woerner@yahoo.com>
To: Niki Denev <nike_d@cytexbg.com>, freebsd-fs@FreeBSD.org
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Subject: Re: Journaling UFS with gjournal.
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--- Niki Denev <nike_d@cytexbg.com> wrote:
> I wonder if it's possible to use gjournal on
> existing file system with the journal on a vnode/(swap?) backed md(4) device?
> (i want to test on a existing installation without free unpartitioned space)
> 
Hmm... I think that would be a not so good idea.

Proof: Consider the follow scenario:
1. journal area A is nearly full, so we switch to journal area B
2. switching to B completed
3. starting to execute update order-requests in area A
4. before requests in area A is completely executed, the power fails
   ==> journal A and B is lost, but file system is not necessarily in a
       consistent state (since A has not been executed completely)

Btw.: I found another big advantage (beside the BIO_FLUSH):
NEVER FSCK AGAIN! ;-)

-Arne

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