Re: raid 1 - automatic 'repair' possible?

[Ric Wheeler <ric@emc.com>]

Having looked at a lot of disks, I think that it is definitely worth 
forcing a write to try and invoke the remap.  With large drives, you 
usually several bad sectors in the normal case (drive vendors allocate 
up to a couple thousand spare sectors just for remapping).

Depending on the type of drive error, the act of writing is likely to 
clean the questionable sector and leave you with a perfectly fine disk.

Ric

Jakob Oestergaard wrote:

>On Wed, Jan 19, 2005 at 11:48:52AM +0100, Kiniger wrote:
>...
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>>some random thoughts:
>>
>>nowadays hardware sector sizes are much bigger than 512 bytes
>>    
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>No :)
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>>and
>>the read error may affect some sectors +- the sector which actually
>>returned the error.
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>That's right
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>>to keep the handling in userspace as much as possible: 
>>
>>the real problem is the long resync time. therefore it would
>>be sufficient to have a concept of "defective areas" per partition
>>and drive (a few of them, perhaps four or so , would be enough) 
>>which will be excluded from reads/writes and some means to
>>re-synchronize these "defective areas" from the good counterparts
>>of the other disk. This would avoid having the whole partition being
>>marked as defective.
>>    
>>
>
>I wonder if it's really worth it.
>
>The original idea has some merit I think - but what you're suggesting
>here is almost "bad block remapping" with transparent recovery and user
>space policy agents etc. etc.
>
>If a drive has problems reading the platter, it can usually be corrected
>by overwriting the given sector (either the drive can actually overwrite
>the sector in place, or it will re-allocate it with severe read
>performance penalties following). But there's a reason why that sector
>went bad, and you realy want to get the disk replaced.
>
>I think the current policy of marking the disk as failed when it has
>failed is sensible.
>
>Just my 0.02 Euro
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