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Date: Tue, 06 Nov 2007 14:53:30 -0700
From: Scott Long <scottl@samsco.org>
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To: John Baldwin <jhb@freebsd.org>
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Cc: Dag-Erling Sm??rgrav <des@des.no>, freebsd-current@freebsd.org,
	Artem Kuchin <matrix@itlegion.ru>, Pawel Jakub Dawidek <pjd@freebsd.org>
Subject: Re: BIO_FLUSH on twe driver. Why is it not there?
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John Baldwin wrote:
> On Friday 02 November 2007 05:55:07 am Pawel Jakub Dawidek wrote:
>> On Thu, Nov 01, 2007 at 10:41:00PM +0100, Dag-Erling Sm??rgrav wrote:
>>> "Artem Kuchin" <matrix@itlegion.ru> writes:
>>>> However, twe is working via scsi subsystem and the authour of gjournal
>>>> said somewhere that he has had implemeneted BIO_FLISH for scsi and he
>>>> specifically mentioned that he has tested twe and twa and they both
>>>> support BIO_FLUSH.
>>> twa(4) uses CAM, but twe(4) doesn't (and never has).
>> That was my mistake. Someone told me (I think it was jhb@), that twe(4)
>> turns off write cache automatically when there is no battery, so
>> BIO_FLUSH isn't really needed and if there is a battery, it also isn't
>> really needed. It would be nice to hide the warning in this case
>> somehow, but for now you should be safe by simply ignoring the warning.
> 
> I have no idea if twe(4) does this.  I do know that both ciss(4) and mfi(4)
> do this.  Possibly amr(4) as well.
> 

MFI can be overridden trivially, and so can AMR, so I don't consider 
them to be good examples.

Scott