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Date:      Thu, 24 Oct 1996 17:34:33 -0400
From:      Bakul Shah <bakul@plexuscom.com>
To:        dg@Root.COM, dwhite@resnet.uoregon.edu, fenner@parc.xerox.com
Cc:        questions@freebsd.org
Subject:   Re: Is my disk going bad? 
Message-ID:  <199610242134.RAA13123@chai.plexuscom.com>
In-Reply-To: Your message of "Thu, 24 Oct 1996 13:41:39 PDT." <199610242041.NAA06512@root.com> 

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> >> I just noticed that I've been getting these for a while:
> >> 
> >>  sd1(ncr0:1:0): MEDIUM ERROR info:119a05 csi:6,a8,3,41 asc:11,43  field replaceable unit: 15 sks:80,40
> >> 
> >> sd1 is a Quantum 1080S.  I don't have the probe messages since the
> >> medium error messages have scrolled them away.
> >> 
> >> I just yesterday turned on remapping:
> >> 
> >> % scsi -f /dev/rsd1 -m 1
> >> AWRE (Auto Write Reallocation Enbld):  1 
> >> ARRE (Auto Read Reallocation Enbld):  1 
> >> 
> >> but it's not remapping, it's still returning errors.
> >> 
> >> Is this the disk going so bad that it can't reallocate to good blocks?
> >
> >How full is it?  Once you've filled the disk then it can't reallocate
> >those bad sectors anywhere else.

>    Uhh, gurp. Drives reserve spare tracks and blocks for use in reallocation.
> The space does not come from the filesystem free block pool.

If the MEDIUM ERROR was a `hard read error', one that can not be
corrected by the block's ECC, the disk is doing the *right thing* by
not automatically remapping it.  If a block with a hard read error
was automatically remapped, the _next_ time this block is read, you
*won't* get a read error but any data in this new block is garbage
-- so now you have _silent_ data corruption.

Automatic remapping only makes sense on a write to a known bad block
or on a *soft read error* -- in the latter case the original data
_was_ recovered thanks to the ECC and on the chance this block is
going bad, the original data is moved to a good block (and the old
block number is mapped to the new block).

Another (remote) possibility is that the disk has run out of spares.



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