Re: [gentoo-user] The sudden disappearance of ....WHAT??? (I/O error on a SD flash card?!)

[Bill Kenworthy]

On 26/03/17 17:24, tuxic@××××××.de wrote:
> On 03/26 04:50, Bill Kenworthy wrote:
>> On 26/03/17 15:26, tuxic@××××××.de wrote:
>>> On 03/26 03:04, Bill Kenworthy wrote:
>>>> On 26/03/17 14:25, tuxic@××××××.de wrote:
>>>>> On 03/26 05:50, tuxic@××××××.de wrote:
>>>>>> On 03/26 11:21, Adam Carter wrote:
>>>>>>> Step 1: dd the contents into an image
>>>>>>>
>>>>>>> ddrescue is probably a better option than plain dd.
>>>>>>>
>>>>>>> step 2: put the sdcard to one side.
>>>>>>>> step 3: loopback mount a copy of the image (not the original)
>>>>>>>> step 4: try recovering the filesystem on the loopback, if it fails ... try
>>>>>>>> something else on another image copy
>>>>>>>
>>>>>>>
>>>>>>> Yep, once you've got the image mounted loopback, you can run
>>>>>>> testdisk/photorec depending on how bad it is.
>>>>>>
>>>>>> Hi all,
>>>>>>
>>>>>> thanks a lot for all help! :)
>>>>>>
>>>>>> Currently I am ddresucueing the flashcard to the harddisc.
>>>>>> Next I will try to mount the sdcard.
>>>>>>
>>>>>> What reliable sdcard-reader can one recommend ?
>>>>>> (...sorry if this sentence sounds harsh...I it by no means meant
>>>>>> that way...I am no native speaker... :)
>>>>>>
>>>>>> Cheers
>>>>>> Meino
>>>>>>
>>>>>>
>>>>>
>>>>> Hi,
>>>>>
>>>>> Is the assumption correct, that -- if ddrescue could read each
>>>>> partitions of the sdcard without stuttering, retries and errors --
>>>>> the sdcard itsself is ok and "only" the logical structure
>>>>> (fs, superblock etc) got damaged?
>>>>> Or do I overlook something?
>>>>>
>>>>> (Background: I dont want to put a sdcard into the bin, if
>>>>> fdisking & reformatting that beast would gives me back an ok
>>>>> media...)
>>>>>
>>>>> Cheers
>>>>> Meino
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>> The dd gets you the best chance to work on the data before it completely
>>>> fails.  In my experience the sdcard will only get worse ending with total
>>>> failure - if it hasn't already.
>>>>
>>>> If the dd dump comes up rubbish and cant be recovered, the actual sdcard
>>>> will be worse.  You can run "strings" against the image to see if there is
>>>> any text in there (or even cat the /dev/sdcard node through strings) to see
>>>> if the bits are still there.
>>>>
>>>> I dont know of a cdparanoia type recovery utility for sdcards but I suspect
>>>> sdcard design means that approach wont work.
>>>>
>>>> BillK
>>>>
>>>>
>>>>
>>>
>>> Hi Bill,
>>>
>>> I got mixed results: There are three partitions on the sdcard from
>>> which I could fully recover (even mount it directly via loop device)
>>> the first and the third one.
>>>
>>> The second one is screwed up.
>>>
>>> Running fsch.ext4 against the image it starts with "bad superblock"
>>> and suggests two alternatives.
>>>
>>> I started fsch.ext4 again while using -b to define the alternate
>>> superblock and it starts to ask me *zillions of question, which
>>> I all answered with 'yes' in a first attempt (I have a backup of the
>>> image...).
>>> The result was an image, which I could mount again.
>>> But beside 'lost+found' with some small rests of something which
>>> may be files in a previous life nothing was there....
>>>
>>> Currently it looks to me, that something has totally messed up the fs
>>> there.
>>>
>>> What do you think?
>>>
>>> Cheers
>>> Meino
>>>
>>>
>>>
>>>
>>>
>> Sounds like its toast :(
>>
>> I have never had a lot of luck with any of the ext file systems - you have
>> to baby them and they corrupt very easily compared to others.  I try and
>> avoid them ...
>>
>> BillK
>>
>>
>>
>
> Hi Bill,
>
> ...the SDcard is for my Android tablet, which runs kernel 3.6.x.something (Lollipop)
> if I remember correctly. With the App Linux Deploy I installed Linux
> on another partition of the sdcard and used to chroot into it.
>
> With what filesystem did you made good experiences of, Bill? My GENTOO PC
> (with which I am currently writing this email) also uses ext4...and
> your last mail makes me nervous...very nervous...
>
> For my tablet I have to use an filesystem, which is supported by and
> compiled into the kernel. Unfortunately, there is no alternative
> Android build for this tablet...
> In this case it is ext4 and vfat...and of that both I think ext4 is
> better...
>
> Cheers
> Meino
>
>

I used to prefer reiserfs ... more robust in some ways, less in others 
... BUT I almost always was able to rescue files or whole filesystems 
with reiserfs, not so with ext*.  These days I prefer btrfs ... again 
not perfect but with OS disks are single and the rest are bcache/ssd 
fronted  btrfs raid10's my main issue is running out of space.

Problems with the ext series were inability to deal with dirvish backup 
(corrupted), running out of inodes, terminal corruption when running out 
of space, silent corruption with hibernation, data loss/corruption on 
abrupt power loss, and it goes on ...


Current sdcards are either vfat for win compatibility (no choice) or 
btrfs (raspberry pi).  Just turned off my older rpi model 1B which is 
ext 4 earlier this morning - been corrupted and reimaged a few times!

File systems seem to be very much YMMV - each use, load and environment 
present a different set of requirements and problems.

BillK