Re: o_sync in vfat driver

On Tue, Feb 28, 2006 at 08:10:44AM -0500, linux-os (*** Johnson) wrote:

On Mon, 27 Feb 2006 col-pepper@xxxxxxxxxxx wrote:

On Mon, 27 Feb 2006 22:32:07 +0100, linux-os (*** Johnson)
<linux-os@xxxxxxxxxxxx> wrote:

Flash does not get zeroed to be written! It gets erased, which sets all
the bits to '1', i.e., all bytes to 0xff.

Thanks for the correction, but that does not change the discussion.

Further, the designers of
flash disks are not stupid as you assume. The direct access occurs
to static RAM (read/write stuff).

I'm not assuming anything . Some hardware has been killed by this issue.
http://lkml.org/lkml/2005/5/13/144

No. That hardware was not killed by that issue. The writer, or another
who had encountered the same issue, eventually repartitioned and
reformatted the device. The partition table had gotten corrupted by
some experiments and the writer assumed that the device was broken.
It wasn't.

Also, if you read other elements in this thread, you would have
learned about something that has become somewhat of a red herring.

It takes about a second to erase a 64k physical sector. This is
a required operation before it is written. Since the projected
life of these new devices is about 5 to 10 million such cycles,
(older NAND flash used in modems was only 100-200k) the writer
would have to be running that "brand new device" for at least
5 million seconds. Let's see:

How come I can write to my compact flash at about 2M/s if you claim it
takes 1s to erase a 64k sector? Somehow I think your number is much too
high. Or it can do multiple erases at the same time.

Also the 5 to 10 million is a lot higher than the numbers the makers of
the compact flash cards I use claim.

60 seconds per minute
3600 seconds per hour
86400 seconds per day.

5,000,000 / 86400 = 57 days of continuous writes to the same
sector. The writer surely would have a strange file because
he states that even a single large file can destroy the drive
if it is mounted with the "sync" option.

Also, the failure mode of NAND flash is not that it becomes
"destroyed". The failure mode is a slow loss of data. The
devices no longer retain data for a zillion years, only a
few hundred, eventually, only a year or so. So when somebody
claims that the flash has gotten destroyed, they need to have
written it for a few months, then waited for a few years before
reporting the event.

Some flash devices can be "destroyed" by loosing power in the middle of
a write, since this causes them to corrupt their table of blocks and
only the manufacturer has the ability to reset that. Fortunately this
doesn't seem like too common a design.

Len Sorensen
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