add warning and example of fake card and repair

I just tested those instructions and successfully repaired a fake card
this way. There were extra steps needed for the real size to be taken
into account.

It also wasn't very clear that `f3probe` would destroy data, so add a
very explicit warning about this.
parent bb202947
Pipeline #13832819 failed with stage
in 5 minutes and 19 seconds
......@@ -167,6 +167,53 @@ card::
Write: 4'51" / 4192321 = 69us
Reset: 324.5ms / 1 = 324.5ms
.. warning:: As the ``--destructive`` flag hints, this will *destroy*
the data on the card, so backup the data elsewhere before
doing those tests.
Note that older versions of :manpage:`f3probe(1)` (6.0 or earlier)
will have trouble doing its job unless the card is connected through a
USB reader. Newer versions can deal with normal block devices,
provided that you pass the magic ``--reset-type=2`` argument. Here's
such an example, on a fake MicroSD card that is labeled and announced
as 32GB but is actually closer to 16GB::
root@curie:/home/anarcat/backup# ~anarcat/dist/f3/f3probe --destructive --time-ops --reset-type=2 /dev/mmcblk0
F3 probe 6.0
Copyright (C) 2010 Digirati Internet LTDA.
This is free software; see the source for copying conditions.
WARNING: Probing normally takes from a few seconds to 15 minutes, but
it can take longer. Please be patient.
Bad news: The device `/dev/mmcblk0' is a counterfeit of type limbo
You can "fix" this device using the following command:
f3fix --last-sec=30983327 /dev/mmcblk0
Device geometry:
*Usable* size: 14.77 GB (30983328 blocks)
Announced size: 31.25 GB (65536000 blocks)
Module: 32.00 GB (2^35 Bytes)
Approximate cache size: 7.00 MB (14336 blocks), need-reset=no
Physical block size: 512.00 Byte (2^9 Bytes)
Probe time: 2'29"
Operation: total time / count = avg time
Read: 1.57s / 32937 = 47us
Write: 2'27" / 200814 = 736us
Reset: 2us / 2 = 1us
To repair the device, you can repartition it quickly with the
:manpage:`f3fix(1)` command, as recommended in the output::
f3fix --last-sec=30983327 /dev/mmcblk0
You will also need to reformat the partition so the new size is taken
into account, for example if this is a FAT32 filesystem::
mkfs.fat /dev/mmcblk0p1
You can also perform bandwidth tests with :manpage:`f3read(1)` and
......@@ -175,7 +222,7 @@ You can also perform bandwidth tests with :manpage:`f3read(1)` and
f3read /media/sdb1
This allows you to detect hidden caches and fake sizes directly as
well. To fix memory cards, use the :manpage:`f3fix(1)` command.
Network performance testing
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