Mark Simmons mds@gbnet.net writes;
James Brigman wrote:
Steve;
Netapp recently modified their disk reconstruct procedure to copy as much valid data as possible from the failed disk and only reconstruct blocks that cannot be read. Often a disk does not completely fail, so many blocks can be copied from it, which is much faster than reconstructing.
Can you please point us to a whitepaper on this?
[...]
I have to say that, if a disk is known to be failing, I'm not sure I'd want to be trusting the data one would copy from it...
Well, there is the "horizontal" data validation provided by the zone or block checksums to deal with that.
Also, if it'sfailing in a way that makes it take a lot of time to serve a block of data, does DOT adjust its strategy accordingly and work out at some point that it should just started recreating the data from the other disks?
That seems like a good question, and I would echo James' request for a whitepaper (or other form of technical detail).
Is the same procedure used when a disk is failed by operator command as well as when ONTAP decides to fail it on its own initiative? The case of failing a disc because its reported error rate is too high for comfort would seem to be one of the most likely scenarios when "many blocks can be copied from it".
Also, if ONTAP is rebooted during the reconstruction, is the "half-failed" status of the disc preserved?
Chris Thompson Email: cet1@cam.ac.uk