question about burning and then reading (dd) to confirm sha256sum

[Pete Travis]

On Apr 2, 2015 2:38 AM, "g" <geleem at bellsouth.net> wrote:
>
>
>
> On 04/01/2015 11:40 PM, Robin Laing wrote:
> > On 2015-04-01 19:15, g wrote:
> >> On 04/01/2015 02:18 PM, jd1008 wrote:
> >>> After burning 3 DVD's, and reading them back to compute sha256sum.
> >>> all three of them generated these error messages during readback,
> >>> and all 3 messages show the error was past the 4gb offset.
> >>>
> >>> Is this a media issue or is it the burner?
> >>
> >> 1- burn dvd at 2 speeds lower than what you used and had failure.
> >>
> >> if ok, problem is either burner or blanks.
> >>
> >> 2- burn dvd at failure speed on a different burner.
> >>
> >> if ok, get a new burner. if failure, may be blanks.
> >>
> >> 3- try different program or burn from command line.
> >>
> >>> A side question: why does the block io layer assume that all media
> >>> have 512 byte sectors?
> >>
> >> i believe that is a carry over from disk formatting started by the
> >> IBM PC. [do not hold me to that]
> >>
> >
> > Also watch power supply voltages.
> >
> > I have ran into two power supplies that caused issues with CD
> > burning. Couldn't supply that little extra bit of current during
> > the burn process. To burners later, I finally found it.
>
> this is true.
>
> a few years back, a poster asked for recommendations on building up
> system and had a lot of responses.
>
> my response of getting a power supply with at least a 20% factor,
> and that a 30% factor would be even better due to my considering
> future additions or changes.
>
> i was met with opposition and even ridicule from a poster who
> stated that he had never seen need.
>
> too many 'builders' are unaware of such factors and will end up
> with a system that gets flaky when additions and upgrades are
> made.
>
> such is a prime reason for 'ready made' failures.
>
> back to dvd checksum errors and a great surprise that i just had.
>
> due to need for centos 6.6 i386 for a system that i am putting
> together for home control use, i decided to burn the iso to a
> dvd rw disk using k3b and all went well including k3b ok'ing
> the burn.
>
> after closing k3b i ran 'sha256sum /dev/sr1 > sr1' with disk still
> in the usb drive i burned it with. checksum failed.
>
> so decided to moved disk to the internal burner to see how it check.
> 'sha256sum /dev/sr0 > sr0' produce correct sha256sum.
>
> having run check on the usb burner many time before when using k3b
> and cl and i have gotten good checks, i was surprised.
>
> am i going to worry about it. hell no. 2 out of 3 good checks tells
> me that Murphy is at it again. ((GBWG))
>
>
> --
>
> peace out.
>
> in a world with out fences, who needs gates.
>
> CentOS GNU/Linux 6.6
>
> tc,hago.
>
> g
> .
>
> --
> users mailing list

After viewing lots of graphs from really serious PSU testing (ie
jonnyguru.com), I decided that "PSUs are most efficient at 50-60% capacity"
was a good enough generalization.  If you work out the maximum draw of your
system, add around 40%, and find a quality! power supply in that range,
you're set.

Emphasis on quality, though.  The dramatically cheaper ones lie, or state
consumption rather than output, use some esoteric metric for wattage specs,
or otherwise aren't actually capable of what they claim.

--Pete
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