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SubjectRe: Journaling pointless with today's hard disks?
Date
----- Original Message -----
From: "Steve Brueggeman" <xioborg@yahoo.com>
To: <linux-kernel@vger.kernel.org>
Sent: Monday, November 26, 2001 7:05 PM
Subject: Re: Journaling pointless with today's hard disks?

<snip>

> >There is no "power monitor" in a PC system (at least not that is visible
> >to the drive) -- if the drive needs it, it has to provide it itself.
> >
> >It's definitely the responsibility of the drive to recover gracefully
> >from such an event, which means that it writes anything that it has
> >committed to the host to write;
> Correct. If a write gets interrupted in the middle of it's operation,
> it has not yet returned any completion status, (unless you've enabled
> write-caching, in which case, you're already asking for trouble) A
> subsequent read of this half-written sector can return uncorrectable
> status though, which would be unfortunate if this sector was your
> allocation table, and the write was a read-modify-write.
>
> >anything it hasn't gotten committed to
> >write (but has received) can be written or not written, but must not
> >cause a failure of the drive.
> Reading a sector that was a partial-write because of a power-loss, and
> returning UNCORRECTABLE status, is not a failure of the drive.

I sure think the drives could afford the teeny-weeny cost of a power failure
detection unit, that when a power loss/sway is detected, halts all
operations to the platters except for the writing of the current sector.

_____________________________________________________
| Martin Eriksson <nitrax@giron.wox.org>
| MSc CSE student, department of Computing Science
| Umeå University, Sweden


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