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3 parity sync errors after removing 2 disks

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Last month's parity sync completed with 0 errors.  Since then, I've installed a new disk and SATA controller.  The disk is an unassigned device and is the only disk connected to the controller.  I cancelled this month's parity sync 3 minutes in because I was planning to zero and remove some smaller disks.  I zeroed two disks (4 & 5) using the dd method.  Each was zeroed one at a time.  Once completed, I stopped the array, performed a new config, preserved all assignments, set disk 4 and 5 unassigned, clicked parity is valid and started the array.  I started a manual parity sync.  When it completed, it reported 3 errors.  I'll re-run another parity sync, but any thoughts on possible cause?  This is first parity error on this server.


dd bs=1M if=/dev/zero of=/dev/md4p1 status=progress
dd bs=1M if=/dev/zero of=/dev/md5p1 status=progress



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2 hours ago, JorgeB said:

Maintenance mode should always be used, unless you manually unmount those disks before doing it, if not a few sync errors are expected.


Thanks.  The docs procedure implies using maintenance mode gives better performance but, isn't necessarily crucial for maintaining parity during a disk clear.  


For best performance, make sure there are no reads/writes happening to the array. The easiest way to do this is to bring the array up in maintenance mode.


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