Date: Mon, 11 Sep 2006 17:37:06 +0200
From: Jens Axboe <axboe@suse.de>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jeff Garzik <jeff@garzik.org>, Sergei Shtylyov <sshtylyov@ru.mvista.com>,
       linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@osdl.org>, Linus Torvalds <torvalds@osdl.org>
Subject: Re: What's in libata-dev.git
Message-ID: <20060911153706.GE4955@suse.de>
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On Mon, Sep 11 2006, Alan Cox wrote:
> Ar Llu, 2006-09-11 am 10:44 -0400, ysgrifennodd Jeff Garzik:
> > > drivers/ide. You might want to do 256 for SATA Jeff but please don't do
> > > 256 for PATA. Reading specs is too hard for some people ;)
> > > 
> > > Some drives abort the xfer, some just choked.
> > 
> > Where in drivers/ide is it limited to 255?
> 
> Being a sensible sanity check it was removed, and that was a small
> mistake. Some 2.4 also has a 256 limit and it broken various transparent
> raid units, older Maxtors(1Gb or so), some IBM drives etc. Got fixed in
> -ac but never in base.
> 
> The failure pattern is pretty ugly too, your box runs and runs and
> eventually you get a linear 256 sector I/O and it all blows up,
> sometimes. The IBM's abort the xfer but the maxtors may or may not get
> it right (its as if half the firmware has the right test).

So this is a confirmed, broken case? Why has no one complained for 2.4
and 2.6?

> We could perhaps do it by ATA version - 255 for ATA < 3 256 for ATA 3+,

Might be sane, yep.

> lots for LBA48 ? Thats assuming you can show 256 sectors is faster than
> 255. I'd bet for normal I/O its unmeasurably small.

255 isn't faster than 256, measurably. But the alignment for "natural"
transfer sizes is much nicer with 256, that's the problem. You really
don't want 248 + 8 going down all the time, for instance. Perhaps it's
not a real problem, but it could be.

-- 
Jens Axboe

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