Date: Sat, 20 Aug 2005 21:47:30 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: anderson@centtech.com Cc: freebsd-hackers@freebsd.org, hselasky@c2i.net Subject: Re: Parking disk drive heads Message-ID: <20050820.214730.56826446.imp@bsdimp.com> In-Reply-To: <4307EA82.7040108@centtech.com> References: <200508201230.37976.hselasky@c2i.net> <20050820.171238.122195775.imp@bsdimp.com> <4307EA82.7040108@centtech.com>
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In message: <4307EA82.7040108@centtech.com>
Eric Anderson <anderson@centtech.com> writes:
: M. Warner Losh wrote:
: > In message: <200508201230.37976.hselasky@c2i.net>
: > Hans Petter Selasky <hselasky@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...
Warner
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