Parking disk drive heads

[Eric Anderson]

M. Warner Losh wrote:
> In message: <4307EA82.7040108 at centtech.com>
>             Eric Anderson <anderson at centtech.com> writes:
> : M. Warner Losh wrote:
> : > In message: <200508201230.37976.hselasky at c2i.net>
> : >             Hans Petter Selasky <hselasky at c2i.net> writes:
> : > : On Saturday 20 August 2005 10:18, Mike Silbersack wrote:
> : > : > On Fri, 19 Aug 2005, Doug Ambrisko wrote:
> : > : > > Flash is nice but it has some issues.  Atleast dropping it isn't one!
> : > : > >
> : > : > > Doug A.
> : > : >
> : > : > I'd be really happy if I could get a USB flash drive to last more than 8
> : > : > months.  Luckily, I started weekly backups after the first failure.  That
> : > : > helped a lot when the second failure happened.
> : > : >
> : > : 
> : > : Flash drives does usually not last more than 10000 writes, per bit, from what 
> : > : I know. Probably you need some kind of special file-system that moves the 
> : > : files around as the write quoute gets used up! Eventually the size of the 
> : > : disk will reach zero, and you have to move the files elsewhere :-) But this 
> : > : is probably off topic.
> : > 
> : > Actually, 10,000 writes per bit is one or two orders of magnitude too
> : > low these days.  It was more typical for the Linear Flash PCMCIA cards
> : > from 10 years ago.  Today, typically flash devices are good for more
> : > like 100,000 or 500,000 writes per cell, and all the fobs you'd buy
> : > these days have built-in wear averaging.  I've tried three times now
> : > to wear out a flash by writing an incrementing counter to a single
> : > location only to give up after weeks of hammering due to external
> : > factors (power failure, network failure, etc).
> : 
> : As a data point, I've been using 64mb compact flash cards (rated at 100k 
> : writes) in about 100 Soekris boxes (running FreeBSD) for about 4 years, 
> : and they are all still working, except for one.  Now, most compact flash 
> : cards are rated at 1 million writes.
> : 
> : And yes, I'm logging to the card and everything..
> 
> The biggest failure mode of CF cards that we've seen in our boxes is
> static zapage.  We get more CF cards back that didn't fsck due to a
> power failure, etc than we do worn out cards, or even static zapped
> ones.  The static zapping usually happens when we're popping the old
> one out and a new one in...  We think we may have seen one power surge
> related failure, but we're unsure.  We've fielded about 1000 CF cards
> over the past 6 years...

Cool, great info - thanks.  If I may, what are these cards doing? 
(anything cool?) - or at least, what company are you working for that 
uses this many for some purpose?  (simply curiousity)

Eric




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Eric Anderson        Sr. Systems Administrator        Centaur Technology
Anything that works is better than anything that doesn't.
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