[H-GEN] Idea for journalling filesystems

Jason Parker-Burlingham jasonp at panix.com
Tue Jul 1 15:19:21 EDT 2003


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Russell Stuart <russell at stuart.wattle.id.au> writes:

[XFS journals on USB flash media]

> The limit is actually the number of write / erase cycles.

> Your typical flash chip can withstand 100k write / erase cycles.  So
> assuming your USB flash device is 32Mb, you will get to write that
> 32Mb approx 50k times.  Ergo you will be able to write approx 1.5Tb
> to your 32Mb flash device before it fails.

Well, I've done some more looking, and found one flash card product
that *may* be suitable, and one other product which looks good but
may not be.

The first is the M-Systems FFD 2.5" IDE Plus, at

   http://www.m-sys.com/content/products/product.asp?PID=26&FILE=ffd25ideplus&FAM=FFD

Its marketing hype says it will take "> 5,000,000" write cycles, and
it comes with a 256MB to 21.5GB capacity.  (Actually 256MB might be a
bit of overkill for this application!)  There are similar products
which have less capacity, lower write cycles, but presumably lower
price.  I may send email to M-Systems and ask about that.

The other solution is their IDE DiskOnChip product, which has drivers
in the Linux kernel sources.  It appears to be some kind of chip which
has a standard female IDE connector on one side.  I'm guessing that it
would take an entire IDE slot, which isn't ideal, and it won't keep
chugging if the IDE subsystem fails, but it doesn't have any
indication of being susceptible to wear in the same way as the flash
products.  The capacities are also a lot lower---16MB to 256MB for the
IDE Pro.  See

   http://www.m-sys.com/content/products/product.asp?PID=17&FILE=DOCIdePro&FAM=doc

I'll probably write back to the list if I get a reply from their staff
after sending some mail about suitability for my purpose and pricing.

It seems kind of a shame to use an IDE channel on this.  I would
really like to find a USB2 solution which was still cheap due to a
smaller size, with a decent lifetime.  We'll see.
-- 
Stay up-to-date on what I'm doing lately:
                                 http://www.panix.com/~jasonp

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