Re: read error on superblock

[dexen deVries <dexen.devries-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi Vyacheslav,


On Tuesday 24 of July 2012 10:26:37 you wrote:
> I am afraid that it is not so good from the end user point of view.
> 
> First of all, the message "mount: /dev/sda3: can't read superblock" can
> confuse user. The reason is bad sectors inside the volume but user is
> informed about impossibility to read superblock.
> 
> Secondly, it is possible situation when it really needs to use a volume
> in the case of presence of bad sectors. And I think that users can
> expect such NILFS behavior because of declared reliability.
> 
> Unfortunately, as I can understand, NILFS hasn't bad blocks table and
> can't process situation of bad blocks presence on volume correctly. It
> means that NILFS interprets bad blocks as exceptional case. But from my
> point of view, it makes sense to interpret bad blocks as usual thing and
> try to work in the presence of ones. For example, fsck potentially can
> check NILFS volume on bad blocks presence, construct bad blocks table
> and save it on the volume.
> 
> I suggest to add "virtual" special file for bad blocks description. It
> can be described by inode in ifile and all bad blocks can be described
> in DAT file as parts of this "virtual" special file. So, as a result,
> NILFS file system driver will have bad blocks table which can be a basis
> for excluding bad blocks from operation and trying to survive in the not
> good device environment.
> 
> What do you think about such idea?

I believe bad sectors to be thing of the past mostly; any decent harddrive 
(probably also any decent SSD) should re-map them after some re-reads. Some 
data & meta-data loss is possible, but overall the FS should be accessible 
again.
I have no idea why my particular HDD did not re-map; perhaps it just takes 
much longer than I gave it.

As a point of reference, XFS does not do bad block management either; however, 
the partition driver of IRIX does bad sector management -- so it is 
implemented one layer below the FS.


I guess it /may be/ possible to use Linux' `dm' driver in such manner.


Cheers,
-- 
dexen deVries

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