[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

Re: need sd card backup on r-pi-3b

On 23/09/17 16:45, Gene Heskett wrote:
On Saturday 23 September 2017 12:26:23 Mark Morgan Lloyd wrote:

On 23/09/17 15:00, Gene Heskett wrote:
I've never had problems with dd provided that the USB->SDcard
adapter's OK: what command are you using?

The usual syntax:
dd  if=somefile bs=512 of=somedevice, and in the case of sd card

Tell us the /exact/ command you're using.

since no 2 are alike so I usually look at the src's declared size in
dmesg and set count=that-5k so it doesn't error out copying a pny
32GB to a Sandisk 32GB.  Etcher, which is faster, has the same
problem & pitches a fit when it can't find room to put the last 10
sectors.  I've had poor luck with sandisk anything though. pny,
samsung is good stuff. So I bought pny last night.

The first thing I'd say is that almost all of the problems I've had
stopped when I changed the card reader. I'm now using one badged
Canyon which specifically has a Micro-SD slot, i.e. I'm no longer
trying to use an adapter which is universally regarded as being

I have 2 vivitar's, both with microsd slots. They work 100% when burning
an image file from armbian jessie so far.
You don't need that bs=512 and trying a sector-by-sector copy on a
device that uses far larger blocks might be unwise. I use bs=128M

I'll give that a shot.

Don't give dd an explicit block count, let it copy everything. That 5k
in particular could be worse than useless since it doesn't correspond
to a physical or logical block size.

no two sd cards, even from the same maker, are exactly the same size due
to bad block replacements before they are even blister packed for sale.
This is the exact reason they ship stripped images that require you
resize them on the machine they will live in. What we dearly need is a
utility to generate the iso shrunken to only that which is actually
used.  Or do we have such a critter and I don't know about it?

I know all that, and I've spent a lot of time talking to these things directly, measuring times, checking pattern-sensitivity and so on.

And I'd remind you that while we're using similar hardware, you're having problems, I'm not. What does that suggest to you? :-)

Zeroing the target device first might help, i.e. copying from

If the source device has been partitioned to be full, then shrink
first the top filesystem and then the top partition to make sure that
what you're copying is substantially smaller than the target device.
Alternatively a useful hack is to set up your source device with an
extra partition at the top, e.g. FAT just in case you want to move
data around between OSes, then you can delete the top filesystem and
partition before using dd and be confident that you won't be doing an
incomplete copy.

Seems like something that could be scripted.

Yes, for example by the script that Raspbian runs on its first startup.

Don't fool around, just make sure that the valid data on the source card is substantially smaller- and I mean 100s of Mb, not a few Kb- than the destination card.

But my suspicion is that you're doing something wrong like trying to copy one partition when you should be copying all partitions. But since you won't give us an example of the command you're using we can't be certain either way on that.

Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]

Reply to: