Does JFFS respect partitions?
jelson at ISI.EDU
Thu Feb 15 06:11:20 EST 2001
David Woodhouse writes:
>Having a read-only partition on the _emulated_ block device doesn't help.
>The blocks of that partition will still be shifted around to perform
>wear-levelling while you write to the other partition. If the NFTL
>filesystem gets corrupted (note the BETA in capital letters in the
>CONFIG_NFTL_RW config option), you've still lost your read-only filesystem.
Interesting - I didn't realize the DOC did internal wear-levelling. I
guess that might mean that there's no point in using JFFS on top of
the NTFL layer anyway?
I appreciate your advice and knowing that readonly partitions are not,
in reality, readonly from the point of view of the actual flash
blocks. Our original (non-Linux) system was split into two partitions
to prevent against corruption of the OS filesystem - we didn't want
the readonly boot partition to stop working due to, say, a poweroff in
the middle of a write to a log file on the writable partition. I
guess I was assuming that, underneath, writes to the DOC sectors were
more or less atomic, and that corruption on that level was much more
unlikely. I was more worried about a long-lived write failing,
e.g. 30 seconds worth of buffer cache in the OS not being flushed
before a poweroff.
>It's also possible to register the DiskOnChip raw flash as two separate MTD
>devices, which is how we 'partition' normal flash. Then you let the NFTL
>code put a filesystem on one of them and use JFFS on the other.
This sounds ideal - how does one do this?
>> Also, what's jffs2? Is it safe to use that, and how is it different?
>Pay no attention to the man behind the curtain.
I don't know the intricacies of the existing jffs2 code or what's left
to implement, but, will a broomstick speed things up for you? :-)
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