[yocto] Question about file systems

[Trevor Woerner]

On Tue, Mar 5, 2013 at 9:20 PM, Paul D. DeRocco <pderocco at ix.netcom.com> wrote:
> So I guess the questions are these: Are ext2, ext3 and ext4 all equally
> likely to need to do an "fsck" after a disorderly shutdown? Do they
> typically take different amounts of time to do an "fsck"? Or is the
> journaling of ext3 and ext4 something that should be avoided on a flash
> drive at all costs, even though my app won't be doing much file access?

With the embedded project I work on, I had started (roughly 7 years
ago) by using ext2 on our flash drive. I too found that my users
always "yanked the cable" instead of trying to perform any sort of
orderly shutdown. Technically this device is meant to run 24/7, but I
found that several of our field reps were convinced they had to
power-cycle after every configuration change (which I still don't
understand... do they do that on their own computers?).

Anyway, with ext2 we would get irrecoverable disk corruption, or at
least enough corruption that the bootup would halt, waiting (forever)
for the user to "run fsck manually" (our device has a total of 4 LEDs
on the front panel as the only feedback, and they don't "come alive"
until user-space starts). So I switched to ext3 around (roughly) 5
years ago and have not once seen an incident of a failed bootup due to
disk corruption/fsck problems.

Yes, it does make the duration of the bootup non-deterministic, but
for our product bootup time is not a priority.

I can't say as to whether ext4 should be used instead of ext3 or which
is better or faster. All I can say is if your users are "yanking the
cable" you may want to stay away from ext2. Also some sort of fsck is
always run on the next bootup when power is cut off unexpectedly.