Sorry if I'm showing ignorance, but could you elaborate more on what he would be trying to achieve here? What you mean by "extract the ubifs to check the fs" part? As said, it may be my ignorance, but I fail to see what exactly he is going to extract (dd won't work on root ubifs, AIUI), and how to check it (no fsck.ubi in existence AFAIK, as ubifs is immune to logical filesystem damage by design).

BTW, in case you meant simply "make a backup of files", I'm afraid the same error will stop his copying operation, just like while tarring. Excluding problematic path from command (be it tar, cp, or whatever) sounds like only option for me.

/Estel

// Edit

As for files for checking root for physical (bad sectors/blocks) damage, I have no knowledge about them (although I suspect that there are things for checking that particular memory type for physical correctness), but i'm pretty sure that neither RescueOS, Meego, nor Ubuntu contains them by default (fixme?).