Re: Screen Resolution in Kubuntu

On 27 May 2007, Tony Houghton uttered the following:

In <4EEF049690%news@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Darren Salt <news@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

(It saves at least a minute here, due to BIOS startup and a pause which
occurs apparently just before scanning the second IDE bus. Then there's the
periodic full check of some partition or other, which happens exactly when
you want a *fast* reboot...)

Don't you always turn that off? AIUI it shouldn't really be necessary
with journalling, although I have known faults to be found in ext3
partitions during (accidental) checks, and lost most of the contents of
an XFS partition once.

The periodic check definitely is necessary with journalling. Filesystem
corruption (or, more accurately, metadata corruption) can happen for
numerous reasons, among them:

- disk hardware intermittent failures (which often lead to entire
sectors being dumped in entirely the wrong place due to head over/
undershoot)
- bus problems (note that the PCI bus has *no* get it *no* validation
that the same data is received as is sent)
- controller or RAM problems (intermittent bitflips, often due to
alpha particle absorption from decay of radioisotopes in the chip
housing, but sometimes caused by solar activity and random
wandering neutrons from secondary radiation, runs at about two
bitflips per month per Gb with current densities)
- crashes during I/O when data has been written out that requires
metadata changes, but the metadata changes have not yet been
written

Only the last of these problems is corrected by journalling (or by
soft-updates, the technically niftier, more efficient, but *vastly* more
complex solution used by BSD's FFS, which basically consists of ordering
all updates such that a failure at any point will still leave metadata
consistent). All the others remain problems --- and with increasing
drive densities and fsck times, some of them will get much more
problematic (notably the effect of overshoot/undershoot).

Val Henson wrote some fascinating stuff on this last year in LWN:
<http://lwn.net/Articles/190222/>. Strongly recommended reading (Val's
unusual in that she's both numbingly smart *and* good at teaching the
craft to newbies).

--
Aiming for 10^10.
.