Re: read error: how to fix?

[Jeff Mahoney <jeffm@suse.de>]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 10/10/2011 11:58 AM, Helmut Hullen wrote:
> Hallo, Jeff,
> 
> Du meintest am 10.10.11:
> 
>>>>> Oct  7 18:16:55 Arktur kernel: ata5.00: exception Emask
>>>>> 0x0 SAct 0x0 SErr 0x0 action 0x0
> 
> [...]
> 
>>> I've just worked again with the 2 unreadable files.
>>> 
>>> Copying them to another partition stopped somewhere, one
>>> time/file at about 98%, the other time at about 2%.
> 
> [...]
> 
>> I'd try replacing the SATA cable and if that doesn't fix it up,
>> you may be out of luck.
> 
> There are 2 unreadable sectors (reproducable). Changing or
> re-mounting the cables doesn't help.
> 
>> The thing is that marking sectors bad is a (pretty poor) band-aid
>> for a much bigger problem: If you're hitting persistent read
>> errors and re-writing the blocks doesn't fix it, your disk is
>> already close to being completely kaput and no amount of software
>> is going to help with that.
> 
> The next steps could be:
> 
> - adding a new 2-TByte disk (now there are 3 2-TByte disks) -
> balancing - removing the bad 2-TByte disk
> 
> But I'm afraid when I run balancing then the bad sectors damage big
>  parts of the contents. I've had such bad luck about 1 year ago,
> losing about 2 TByte of data (ok - I had a kind of backup in a
> neighbout town). I don't like to reproduce this experience.
> 
> I'm afraid I have to buy 3 (or 4) 2-TByte disks, building them as a
> new raid0-data cluster and copy the complete contents from the old
> cluster to the new one. Doesn't sound good.
> 
> -----------------------
> 
> 2 bad sectors from a total of 4*10^9 sectors is (in another point
> of view) no bad error rate ...

Well, it's worse than that. The disk will try to correct for bad
sectors itself internally and will remap them. By the time you start
to see bad sectors on disk (where writing and then reading fails), the
disk's internal remap table has been filled. That hides the true
defect rate but it also means that it's only a matter of time before
you get more bad sectors.

- -Jeff

- -- 
Jeff Mahoney
SUSE Labs
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.18 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

iEYEARECAAYFAk6YkbwACgkQLPWxlyuTD7LrTACeJFBbYZtJrUVBwDM8+R2BBrHS
moIAn3wIZd2Q9TEo8mUkAhVtdZnHgYdr
=hpBv
-----END PGP SIGNATURE-----