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[linux-lvm] Re: [PATCH] 64 bit scsi read/write



At 4:04 PM -0600 2001-07-13, Andreas Dilger wrote:
**) As I said in my previous posting, it depends on if/how MD RAID does
   write ordering of I/O to the data sector and the parity sector.  If
   it holds back the parity write until the data I/O(s) are complete, and
   trusts the data over parity on recovery, you should be OK unless you
   have multiple failures (i.e. bad disk + crash).  If it doesn't do this
   ordering, or trusts parity over data, then you are F***ed (I doubt it
   would have this problem).

That wouldn't help, would it, if >1 data sectors were being written.


The fault mode of a sector simply not being written seems like a real weak point of both RAID-1 and RAID-5. Not that RAID-5 parity ever gets checked, I think, under normal circumstances, nor RAID-1 mirrors get compared, but if they were check and there was an parity or mirror-compare error and no other indication of a fault (eg CRC), there's no way to recover correct data.
--
/Jonathan Lundell.



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