magic sysrq keys functionality

[Scott Long]

On Mon, 26 Jul 2004, Brian Fundakowski Feldman wrote:
B> On Sun, Jul 25, 2004 at 09:23:36PM +0000, bugghy wrote:
> > Yeah but it sometimes "freezes" (no reboot) ... and I'd rather umount my
> > filesystems before rebooting.
>
> SoftUpdates guarantess that your file systems will not get corrupt.
>

This isn't entirely correct.  Softupdates guarantees that you won't get
corruption due to metadata pointing to invalid or stale data blocks.
That's not the same as guaranteeing that there won't be any corruption.
Write caching on the drive combined with an in-opportune power loss or
other failure can easily leave you with corrupt or incomplete metadata
and/or data blocks.  A panic while metadata is being committed to disk can
also leave the metadata highly inconsistent and prone to corruption.
This isn't to say the SU is bad or that other strategies are necessarily
better, just that there are definite risks.

Scott