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Date:      Wed, 20 Apr 2011 23:50:00 +0300
From:      Alexander Motin <mav@FreeBSD.org>
To:        =?ISO-8859-1?Q?Ulrich_Sp=F6rlein?= <uqs@spoerlein.net>
Cc:        FreeBSD-Current <freebsd-current@freebsd.org>
Subject:   Re: Switch from legacy ata(4) to CAM-based ATA
Message-ID:  <4DAF46F8.9040004@FreeBSD.org>
In-Reply-To: <20110420203754.GM85668@acme.spoerlein.net>
References:  <4DAEAE1B.70207@FreeBSD.org> <20110420203754.GM85668@acme.spoerlein.net>

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Ulrich Spörlein wrote:
> Can we then please get the "ad" device prefix back? I seem to remember
> that when they were introduced they were thought to be a temporary thing
> ...
> 
> Unless both stacks can run in parallel, I don't see a problem with
> having them both show up as /dev/ad0, etc. People with problems must
> send in a complete dmesg anyway, so it should be clear what stack they
> are running. The POLA violation for people upgrading from 8.x to 9.0
> however is pretty big ... and unnecessary.

Stacks do can run in parallel, and it really happens when people loading
ahci(4) driver for SATA disks without using `options ATA_CAM` of ata(4)
for PATA. As result, SATA will use new stack and PATA - old one.

What's about POLA violation, it is inevitable, because present kernel
uses ata(4) with ATA_STATIC_ID option, that is not applicable in modern
SATA world order. So at least device numbers will change.

Also you should take into account, that many people and some software
already adapted to adaX names and change back will break POLA for them.

-- 
Alexander Motin



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