[Server-devel] ext2 vs ext4 vs exFAT for XO content SD cards?

[Sameer Verma]

James,
Would it help to mark the content partition(s) as read only?

Sameer
On Aug 16, 2015 5:13 PM, "James Cameron" <quozl at laptop.org> wrote:

> 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/
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> Server-devel at lists.laptop.org
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>
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