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From: Hubert Kario <>
To: Paul Millar <>
Subject: Re: A couple of questions
Date: Wed, 2 Jun 2010 18:19:26 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Monday 31 May 2010 19:59:46 Paul Millar wrote:
> Hi Hubert,
> On Thursday 27 May 2010 16:56:00 Hubert Kario wrote:
> > > Would [obtaining file checksum] be possible (without an awful lot
> > > of work)?
> >=20
> > [Calculating checksum in-memory]  won't detect in-memory corruption
> > though, but if you want to be resilant to this, you should be looki=
ng at
> >=20
> >  ECC RAM as subsequent checks can be affected by it to.
> Certainly ECC RAM will help, but unfortunately it doesn't remove the
> possibility of corruption; for example, CERN found [1] that double-bi=
> memory corruptions (which ECC cannot recover from) can still happen.
> [1]
> erialId=3Dpaper&confId=3D13797
> Also, IIRC there was a case where Fermilab tracked down a data corrup=
> to a faulty PCI bus in the server.  So who knows where are all the pl=
> corruption could occur?
> I guess the real problem is that, when processing large amounts of da=
> these rare occurrences start to stack up.

Yes, but AFAIK btrfs checksums don't have internal checksum (e.g. you c=
check if the read checksum is a valid one or not, it does not have cont=
bits), as such, if you consider PCI bus corruption as likely, you still=
get 100% certanity that the data reached the HDD unharmed.

If you need such level of certanity when recording data, I'd consider=20
mainframe hardware and/or duplicating whole storage stack.

Hubert Kario
QBS - Quality Business Software
02-656 Warszawa, ul. Ksawer=C3=B3w 30/85
tel. +48 (22) 646-61-51, 646-74-24

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  reply	other threads:[~2010-06-02 16:19 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-05-27 13:39 A couple of questions Paul Millar
2010-05-27 14:56 ` Hubert Kario
2010-05-31 17:59   ` Paul Millar
2010-06-02 16:19     ` Hubert Kario [this message]
2010-05-27 16:00 ` Chris Mason
2010-05-31 18:06   ` Paul Millar
2010-05-31 20:33     ` Mike Fedyk
2010-06-02 11:56       ` Paul Millar
2010-06-01 13:39     ` Martin K. Petersen
2010-06-02 13:40       ` Paul Millar
2010-06-04  1:17         ` Martin K. Petersen

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