Re: soft update vs journaling?

[Matthias Andree <matthias.andree@gmx.de>]

On Mon, 23 Jan 2006, John Richard Moser wrote:

> The idea of Soft Update was to make sure that while you may lose
> something, when you come back up the FS is in a safely usable state.

Soft Updates are *extremely* sensitive to reordered writes, and more
likely to be reordered at the same time than streaming to a linear
journal is. Don't even THINK of using softupdates without enforcing
write order. ext3fs, particularly with data=ordered or data=journal, is
much more forgiving in my experience. Not that I'd endorse dangerous use
of file system, but the average user just doesn't know.

FreeBSD (stable@ Cc:d) has no notion of write barriers as of yet as it
seems, wedging the SCSI bus in the middle of a write sequence causes
major devastations with WCE=1, and took me two runs of fsck to repair
(unfortunately I needed the (test) machine back up at once, so no time
to snapshot the b0rked partition for later scrutiny), and found myself
with two hundred files relocated to the lost+found office^Wdirectory.

Of course, it's the "Doctor, doctor, it always hurts my right eye if I'm
drinking coffee" -- "well, remove the spoon from your mug before
drinking then" (don't do that) category of "bug", but it hosts practical
relevance...

-- 
Matthias Andree
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