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:: ...@@ -167,6 +167,53 @@ card::
Write: 4'51" / 4192321 = 69us Write: 4'51" / 4192321 = 69us
Reset: 324.5ms / 1 = 324.5ms 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 You can also perform bandwidth tests with :manpage:`f3read(1)` and
:manpage:`f3write(1)`:: :manpage:`f3write(1)`::
...@@ -175,7 +222,7 @@ 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 f3read /media/sdb1
This allows you to detect hidden caches and fake sizes directly as This allows you to detect hidden caches and fake sizes directly as
well. To fix memory cards, use the :manpage:`f3fix(1)` command. well.
Network performance testing Network performance testing
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