ext2 vs ext4 vs exFAT for XO content SD cards?

[James Cameron]

Thanks, interesting questions.

No, ext4 is not a slow journaled filesystem, and no, there are no
obvious problems on SD when using ext4 given your use case.  But it
isn't operating system portable, and as your content is static no need
for a journal.  Other features of ext4 make mounting or filesystem
check faster.

Yes, wear-leveling is taken care of by the firmware in the card, put
there by the manufacturers.  Wear-levelling also critical during
reading, since a flash page can't be read repeatedly without
disturbance eventually requiring it to be written to a freshly erased
page.  This is all handled by the firmware.  Happens way more
frequently than it does on a hard drive.

Duplication time of SD cards won't be affected by your filesystem or
partition decision.

One partition is sufficient.  MBR partition type best, for
compatibility across the operating systems.

For filesystem, use FAT32, mounted read-only.  FAT32 works across most
Windows and Mac computers, at media sizes up to 2 TB, for file sizes
up to 4 GB.

Where content cannot live on FAT32 due to file name character set or
metadata, it can be placed in disk image bundles of ISO-9660,
squashfs, or ext4 and loop mounted.  The content curation process for
the end user might be easier if bundles can be added and removed as
needed.

What you might be overlooking; I/O bandwidth of the connection to the
media, endurance impact of reading data from the card slowing
performance one year on, backups, content bundle tamper checks, risk
of filesystem format incompatibilities introduced by new versions of
operating systems after your product is in the field, risk of cross
system malware infections, electrostatic discharge damage to the card,
and how modern cards can change performance behaviour as a result of a
production state awareness flag stored by card firmware.

On the other hand the alternatives have their own problems.

-- 
James Cameron
http://quozl.linux.org.au/