Re: data loss on jffs2 filesystem on dataflash

jscottkasten_at_yahoo.com
Date: 09/22/05

  • Next message: Ari Sundholm: "Kernel 2.6.14-rc2 compile error" 
    Date:	Thu, 22 Sep 2005 11:43:24 -0700 (PDT)
To: "linux-os (*** Johnson)" <linux-os@analogic.com>, "Artem B. Bityutskiy" <dedekind@yandex.ru>

    Actually, 3 years ago, I researched this in my
    company's lab. There is about a 1 in 180 probability
    of the power to the read/write head failing before the
    sector write is complete.

    The end result is a sector that fails ECC check. The
    linux kernel reports this and your I/O operation
    returns with an error.

    Not easy, but if you force a rewrite of the sector,
    the problem cures itself. Not easy to do through the
    VFS though. I was only able to make it happen by
    using dd if=/dev/zero on the unmounted device node.
    After that, the sector read just fine.

    -Scott Kasten-

    --- "linux-os (*** Johnson)" <linux-os@analogic.com>
    wrote:

    >
    > On Thu, 22 Sep 2005, Artem B. Bityutskiy wrote:
    >
    > > Valdis.Kletnieks@vt.edu wrote:
    > >> On Thu, 22 Sep 2005 14:48:39 +0400, "Artem B.
    > Bityutskiy" said:
    > >>
    > >>> Joern meant that if HDD starts a block write
    > operation, it will
    > >>> accomplish it even if power-fail happens
    > (probably there are some
    > >>> capacitors there). So, it is impossible, say,
    > that HDD has written one
    > >>> half of a sector and has not written the other
    > half.
    > >>
    > >> Hard drives contain capacitors to prevent writing
    > of runt sectors on
    > >> a powerfail? Didn't we go around this a while
    > ago and decide it's mostly
    > >> urban legend, and that plenty of people have seen
    > runt/bad sectors?
    > >
    > > No idea. But theoretically it should be so, at
    > least "good" drives
    > > should. May be a competent person will comment on
    > this, that's quite
    > > interesting.
    > >
    > > --
    > > Best Regards,
    > > Artem B. Bityuckiy,
    > > St.-Petersburg, Russia.
    >
    > The only significant energy storage that hard disks
    > contain
    > is the inertia of the rotating disk assembly. Since
    > the platter
    > motor is not a generator it doesn't help. Those tiny
    > bypass
    > capacitors you see can't store enough energy to do
    > anything
    > useful during a power failure.
    >
    > BUT... The PC/AT power supplies store a lot of
    > energy and
    > they run for many milliseconds after a power fail.
    > 2-100 uF in series = 50 uF @ 300 v.
    > J = 1/2 CV^2
    >
    > J = 50uF * 300^2 / 2 = 2.25 joules (lots of
    > energy).
    >
    > If the power-fail line is properly connected and if
    > the
    > power fail line operates at the correct time, the
    > CPU
    > will be halted while there is still enough energy
    > available
    > to complete any write that has gotten to the
    > disk-drives sector
    > buffer. This does not protect data, but it should
    > certainly
    > protect the sectors which might now contain header,
    > good data
    > or junk, and a proper CRC. IOW a good sector.
    >
    > Cheers,
    > *** Johnson
    > Penguin : Linux version 2.6.13 on an i686 machine
    > (5589.55 BogoMips).
    > Warning : 98.36% of all statistics are fiction.
    >
    >
    ****************************************************************
    > The information transmitted in this message is
    > confidential and may be privileged. Any review,
    > retransmission, dissemination, or other use of this
    > information by persons or entities other than the
    > intended recipient is prohibited. If you are not
    > the intended recipient, please notify Analogic
    > Corporation immediately - by replying to this
    > message or by sending an email to
    > DeliveryErrors@analogic.com - and destroy all copies
    > of this information, including any attachments,
    > without reading or disclosing them.
    >
    > Thank you.
    > -
    > To unsubscribe from this list: send the line
    > "unsubscribe linux-kernel" in
    > the body of a message to majordomo@vger.kernel.org
    > More majordomo info at
    > http://vger.kernel.org/majordomo-info.html
    > Please read the FAQ at http://www.tux.org/lkml/
    >

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

  • Next message: Ari Sundholm: "Kernel 2.6.14-rc2 compile error"
    Loading