Date: Thu, 26 Sep 2002 21:09:47 +0200 From: Alexander Leidinger <Alexander@Leidinger.net> To: Terry Lambert <tlambert2@mindspring.com> Cc: freebsd-current@FreeBSD.ORG Subject: Re: Journaled filesystem in CURRENT Message-ID: <20020926210947.5d5fdd45.Alexander@Leidinger.net> In-Reply-To: <3D93459B.E4405568@mindspring.com> References: <200209251319.g8PDJYoD047918@ib.com.ua> <20020925111232.B3686@Odin.AC.HMC.Edu> <20020926111949.5c0da160.Alexander@Leidinger.net> <20020926090325.A24614@zardoc.esmtp.org> <3D93459B.E4405568@mindspring.com>
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On Thu, 26 Sep 2002 10:36:27 -0700 Terry Lambert
<tlambert2@mindspring.com> wrote:
> That said, journalling and Soft Updates are totally orthogonal
> technologies, just as btree and linear directory structures are
> two orthogonal things.
>
> Journalling has advantages that a non-journalling FS with soft
> updates does not -- can not -- have, particularly since it is
> not possible to distinguish a power failure from a hardware
> failure from (some) software failures, and those cases need to
Power failure:
No problem for both.
Hardware failure (I assume you think about a HDD failure):
Read failure: doesn't matter here
Write failure: either the sector gets remapped (no problem
for both), or the disk is in self destruct
mode (both can't cope with this)
Software failure:
Are you talking about bugs in the FS code? Or about a nasty
person which writes some bad data into the FS structures?
> be treated differently for the purposes of recovery. The soft
Sorry, I don't get it. Can you please be more verbose?
> updates background recover can not do this; the foregound
> recovery can, but only if it's not the abbreviated version. A
What are you talking about? Did you managed to get an unexpected
softupdates inconsistency after the last bugfix?
I don't see a difference in the power or hardware failure cases for a
journaled fs and SO. The only reason for a fg-fsck instead of a bg-fsck
(in the "there's no bug in the bg-fsck code path" case) is if someone
damages the fs-structures on disk (I assume there are no bugs in SO
anymore which result in an unexpected SO inconsistency).
Note: I don't think the actual code path for bg-fsck is bugfree at the
moment (read: I don't trust it at the moment).
> JFS that journals both data and metadata can recover from all
> three, to a consistant state, and one that journals only
> metadata can recover from two of them.
SO writes the data directly to free sectors in the target filesystem. I
don't see where journaled data is an improvement in fs-consistency here.
Bye,
Alexander.
--
It's not a bug, it's tradition!
http://www.Leidinger.net Alexander @ Leidinger.net
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