[yocto] Question about file systems

[Rudolf Streif]

There is a major difference between ext3 and ext4 which is called "delayed
(block) allocation." Delayed allocation of blocks increases the risk of
data loss in certain circumstances. While ext3 typically syncs cache to
disk every 5s, it can take 2min with ext4.





On Wed, Mar 6, 2013 at 10:20 AM, Trevor Woerner <twoerner at gmail.com> wrote:

> 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.
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*Rudolf J. Streif*
Director of Embedded Solutions
The Linux Foundation

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