Date: Thu, 6 Jul 2000 12:37:34 +0200
From: Ookhoi <ookhoi@dds.nl>
> In article <cistron.20000706093557.F13402@ookhoi.dds.nl>,
> Ookhoi <ookhoi@dds.nl> wrote:
> >Why not use Reiserfs? I think journaling is a must with disks that
> >large, and reiserfs is faster dan ext2 if you have a lot of files/dirs
> >in a directory.
>
> Ehrm. Look at the subject of this thread. What do you think "ext3" is ;)
Yeah, I know, but then again, why do they all want to fsck? We have so
many nice journaling file systems now.
1) Ext3 is a journaling filesystem.
2) Even with journaling filesystems, there will be cases you will need
to run some kind of filesystem consistency checker.
a) In case of disk drive problems.
b) In case of memory problems (particularly cache memory)
c) In case of kernel bugs (many times what people think of as
"bugs" in filesystem code is really bugs in the VM or
buffer cache parts of the kernel.)
This is true for all journaling filesystems; they aren't magic.
What journaling filesystems do protect you against is the need to
run fsck in case of an power failure or a kernel crash, or some
other kind of unclean shutdown (so long as that unclean shutdown
doesn't cause any other forms of on-disk corruption.)
3) For example, I have seen reports that sound like there are
problematic hard disk subsystems out there that will write garbage
out to disk during an unclean shutdown. (i.e., as the voltage on
the power rail starts going down, the memory is the most sensitive
to voltage drops, and fails first by writing garbage out to the
memory bus. Meanwhile, the hard drive controller continues to
happily DMA'ing said garbage to the disk.)
The cases where I've seen this is reports of major parts of the
inode table getting trashed in ext2 when all that happened was an
unclean shutdown. I've gotten enough reports of this out there that
I'm pretty sure it's not a fluke, and there are systems out there
that have this unfortunate characteristic if the disk is being
written when someone unkindly hits the Big Red Button.
If your hardware is doing nasty things like this, no amount of
journaling filesystem is going to save you.
Don't get me wrong; journaling filesystems are good stuff, and they're
definitely something that we'd should have. It's just that there are a
lot of people who seem to be ascribing almost mythic powers to
journaling filesystems, and that's a bad thing. Journaling is a
technology, nothing more and nothing less.
- Ted
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This archive was generated by hypermail 2b29 : Fri Jul 07 2000 - 21:00:18 EST