Smartd message: What does it mean?

[Peter Arremann]

On Friday 28 October 2005 22:26, Danny Terweij - Net Tuning | Net wrote:
> Hi
>
> I have 2 machines with such messages  and hdd's just running fine for 2+
> years. If ext2/3 fs is not marking such sectors as "bad, i dont use it
> anymore" then its about time that such things are going to be developed
> right? I do not want to replace a HDD if just 1 sector is marked bad at
> smartd. The smartd message is only showing up after a reboot overhere.
>
> Danny.
>From the man page of smartd:
A pending sector is a disk sector (containing 512 bytes of your data) which 
the device would like to mark as ``bad" and reallocate. Typically this is 
because your computer tried to read that sector, and the read failed because 
the data on it has been corrupted and has inconsistent Error Checking and 
Correction (ECC) codes. This is important to know, because it means that 
there is some unreadable data on the disk. The problem of figuring out what 
file this data belongs to is operating system and file system specific. You 
can typically force the sector to reallocate by writing to it (translation: 
make the device substitute a spare good sector for the bad one) but at the 
price of losing the 512 bytes of data stored there.


In other words, the data that's there is already gone (unless in some very 
rare cases reallocating works later).  What is ext2/3 supposed to do about 
that? The drive is supposed to take care of it and remap to a spare sector. 
Look at hdparm -D . Scsi drives willingly reveal their defect list - Not sure 
how to read it on an ide disk though.

The main reason for worrying about a single sector is that this is a sector 
that has failed not just one read, but all read attempts made by the drive. 
If it was a soft error and eventually the drive had recovered the data then 
you'd just see the info if you use smartctl - but you don't have any 
immediate issues. No drive is perfect and some remapping always goes on. 
If you however  have a hard error and have pending sectors its a sign that 
something more serious than normal use has happened with the drive and now it 
is not a question of IF your drive fails but if you got a day or a week or a 
month before it really goes. Many people are lucky but in the office (where 
we've got about 400 linux boxes, many with more than 1 drive) the stats show 
that between the first pending sectors and the final drive failure its an 
average of about 5 weeks. Enjoy :-) 

Anyway, reallocation of blocks is something the drive has to handle not the 
filesystem.

Peter.

>
> ----- Original Message -----
> From: "Daniel B. Thurman" <dant at cdkkt.com>
> To: "For users of Fedora Core releases" <fedora-list at redhat.com>
> Sent: Saturday, October 29, 2005 4:18 AM
> Subject: RE: Smartd message: What does it mean?
>
>
>
> Hmmm...  or does it mean I need to completely
> reformat or fsck this disk throughly to ensure
> that it is really going bad?  I am using FC4
> so I wonder if there is another reason...
>
> I will have to chek this out.
>
> Dan
>
> -----Original Message-----
> From: fedora-list-bounces at redhat.com
> [mailto:fedora-list-bounces at redhat.com]On Behalf Of Benjamin Franz
> Sent: Friday, October 28, 2005 7:10 PM
> To: For users of Fedora Core releases
> Subject: Re: Smartd message: What does it mean?
>
> On Fri, 28 Oct 2005, Daniel B. Thurman wrote:
> > Hi Folks,
> >
> > Trying to understand this message, any ideas?
> >
> > This email was generated by the smartd daemon running on:
> >
> >   host name: xxx.xxx.com
> >  DNS domain: xxx.com
> >  NIS domain: (none)
> >
> > The following warning/error was logged by the smartd daemon:
> > Device: /dev/hdb, 14 Currently unreadable (pending) sectors
> > For details see host's SYSLOG (default: /var/log/messages).
>
> It means you have 14 bad sectors on your /dev/hdb hard drive. It also
> means it is time to buy another drive and copy your data over to it.
>
> --
> Benjamin Franz
>
> The designer of a new kind of system must participate fully in the
> implementation.
>
>                                                           - Donald E. Knuth
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