Re: raid 1 - automatic 'repair' possible?

From: Ric Wheeler (ric_at_emc.com)
Date: 01/28/05

  • Next message: Dmitry Torokhov: "Re: atkbd_init lockup with 2.6.11-rc1" 
    Date:	Fri, 28 Jan 2005 11:39:58 -0500
To: Jakob Oestergaard <jakob@unthought.net>

    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:
    >...
    >
    >
    >>some random thoughts:
    >>
    >>nowadays hardware sector sizes are much bigger than 512 bytes
    >>
    >>
    >
    >No :)
    >
    >
    >
    >>and
    >>the read error may affect some sectors +- the sector which actually
    >>returned the error.
    >>
    >>
    >
    >That's right
    >
    >
    >
    >>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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