[NTLUG:Discuss] External Hard Drive Recommendation

[Darin W. Smith]

Having written flash drivers (for VxWorks) before, I feel I might be able 
to comment a little here, especially regarding life-span.

Life-span is typically quoted in "write cycles" or "erase cycles".  
Typically, it is actually the erase that you worry about (because to 
overwrite something, you have to erase it).  After a flash chip has been 
erased too many times, the contents become locked, and it cannot be erased 
anymore...it is then a ROM, with whatever was last on there.

But, it can happen to different areas of a flash at different times, 
depending on how often that area has been hit.  Some devices (notably, the 
Disk-on-Chip) or filesystems (TFFS, in the case of DOC) excercise "write- 
leveling" or "wear-leveling"...meaning that new data is written to a 
different area, and then the old file location is erased (that's also 
better for data-integrity).  It is done with some statistics being tracked, 
so that you wear the whole chip evenly...this can really help extend the 
life of your flash.

Many are good up into the hundreds of thousands of write/erases, and a few 
*are* good for over a million.  They are getting better all the time, 
though they are still quite slow.

I wouldn't worry too much about that.  I've seen them go for months in 
heavy use with live filesystems running on them.

You definitely should minimize erases (and therefore file updates) as much 
as possible.

As for drivers, I haven't tried any of the encapsulated USB flash devices, 
but I have used a couple of USB compact flash readers.  The easiest to get 
going was a Sandisk Imagemate II.

I also got a Dane-Elec Zmate going with a driver that is not quite in the 
official kernel yet.

That part of the world is definitely not as plug-n-play as it needs to be 
on Linux yet.  You still many times have to do things like unload and 
reload the driver to change media...you also tend to need to run some scsi 
translator modules in order to make them work.  I'd assume the same is true 
for encapsulated flash USB devices...they all work through the usb-storage 
driver (and so would a USB harddrive for that matter, though I think that 
would be well supported, as they could just send the familiar drive 
commands, rather than having to reverse-engineer the proprietary flash 
controller).

-- 
D!
Darin W. Smith
AIM: JediGrover