Date:	Wed, 06 Dec 2006 23:01:54 +0100
From:	Matthias Schniedermeyer <ms@...d.de>
To:	linux-kernel@...r.kernel.org, usb-storage@...ts.one-eyed-alien.net
Subject: single bit errors on files stored on USB-HDDs via USB2/usb_storage

Hi


I'm using a Bunch auf HDDs in USB-Enclosures for storing files.
(currently 38 HDD, with a total capacity of 9,5 TB of which 8,5 TB is used)

After i realised about a year(!) ago that the files copied to the HDDs
sometimes aren't identical to the "original"-files i changed my
procedured so that each file is MD5 before and after and deleted/copied
again if an error is detected.

My averate file size is about 1GB with files from about 400MB to 5000MB
I estimate the average error-rate at about one damaged file in about
10GB of data.

I'm not sure and haven't checked if the files are wrongly written or
"only" wrongly read back as i delete the defective files and copy them
again.

Today i copied a few files back and checked them against the stored MD5
sums and 5 files of 86 (each about 700 MB) had errors. So i copied the 5
files again. 4 of the files were OK after that and coping the last file
the third time also resulted in the correct MD5.

This time i kept the defective files and used "vbindiff" to show me the
difference. Strangly in EVERY case the difference is a single bit in a
sequence of "0xff"-Bytes inside a block of varing bit-values that
changed a "0xff" into a "0xf7".
Also interesting is that each error is at a 0xXXXXXXX5-Position

Attached is a file with 5 of the 6 differences named 1-5. Of each of the
5 2x3 lines-blocks the first 3 lines are the original the following 3
lines contain the error in the middle row 6th value.

NEVER did i see any messages in syslog regarding erros or an aborting
program due to errors passed down from the kernel or something like that.

Data for the computer/software:
Hardware:
Computer is a Dual P3-933Mhz with 3GB (ECC) SD-RAM, Severworks HE-SL-Chipset
Source-HDD is a 200GB S-ATA device connected to a Promise TX-4 using libata.
Destination-HDDs: Several different models in several different
enclosures and different chipsets, mostly Genesys Logic)
USB-controller: Currently i use a EHCI/OHCI-NEC-Chipset add-on card but
since about 4-5 month ago i used a EHCI/UHCI-VIA-Chipset add-on card
with same results.
Software:
Kernel: <What was current 1 year ago> up to 2.6.18, self compiled
vanilla kernels.
I haven't tried 2.6.19 and i don't expect any changes from it.
Distribution: Debian SID


I you need any other information i will provide them as good as i can.




Bis denn

-- 
Real Programmers consider "what you see is what you get" to be just as
bad a concept in Text Editors as it is in women. No, the Real Programmer
wants a "you asked for it, you got it" text editor -- complicated,
cryptic, powerful, unforgiving, dangerous.


View attachment "errors.txt" of type "text/plain" (2396 bytes)

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