Re: easy project? apple scsi hd on a card ie..scsi expander

[mjmahon@aol.com (Michael J. Mahon)]

Sheldon Simms wrote:

>On Tue, 10 Feb 2004 22:07:16 -0500, Bill Garber wrote:
>
>> Sandisk claims that their CF cards do that automatically and
>> rewrite the data on the sectors reaching their limit to new
>> sectors marking the old ones as bad,
>
>If that's true, then it's nice, but doesn't really solve the
>problem.
>
>> and that is only after more than 10,000 writes. Which means
>> you'd have to write the sector nearly 30 times per day for
>> more than a year.
>
>It's true that most sectors wouldn't be written that often, but
>in ProDOS, almost any change anywhere on the disk results in
>writes to the volume bitmap sectors and the beginning of the
>"disk". Just a few file operations can write the bitmap sectors
>many times.
>
>What would be nice for flash "disks" would be a hacked ProDOS
>that tries to spread out the bitmap on the "disk" so that no
>single sector is written repeatedly.

CF cards already do wear levelling for heavily used blocks.

This is done because most file systems (like FAT) have the
same problem with concentrated updates.

Apparently, the problem is solved for all practical purposes,
by the combination of wear levelling and increased endurance
for flash memories in the last few years.

Having said that, it is true that most CF memory is used
for "removeable disk" storage, and not for "resident drive"
applications.  The Apple II community is now begninning to
accumulate experience with this usage with the CFFA card
and the ProDOS OS.  It will be interesting to see how the
rubber meets the road.

-michael

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