On 07/01/2019 11:13, Andrew Gabriel wrote:
> Journals and fsck are designed to handle failures of hard drives.
> Failures of cheap flash (a.k.a. SD cards and USB thumb drives) are
> different in nature, and neither a journal nor fsck are going to be
> able to help. The typical catastropic failure is when the card fails
> to save the logical to physical mapping table back to the flash.
> This has the effect of shuffling a large number of blocks on the disk,
> many of which were written ages ago.

Thumbs up, this can't be pointed out enough.

> Some flash devices will go dead
> at this point, others will just serve up wrong blocks all over the
> place. That's not something journals nor fsck can recover. (I did let
> fsck try once - it just got the drive into a hopeless mess.)
>
> Enterprise flash products go to some length to avoid this catastrophic
> failure mode.

I've found Samsung SD cards start going read only when getting close to
end of life, but seemingly no fsck errors. If you replace then
immediately you are ok. If you reboot they'll go back to r/w, but
they'll go r/o more often, and files will start getting corrupted.
Eventually they wont come out of read only.

The only thing you can do with SD cards is keep them backed up
constantly, and restore to a new card immediately there are any signs of
trouble.

---druck

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