raid 5 mdadm drive dropped whilst growing

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http://serverfault.com – I have a 4x 2tb raid 5 mdadm array which I had begun to grow onto a 5th disk. ~# mdadm --add /dev/md1 /dev/sdb ~# mdadm --grow /dev/md1 --raid-devices=5 midway through the grow I recieved this in an email; A Fail event had been detected on md device /dev/md/fubox:1. It could be related to component device /dev/sdf. Faithfully yours, etc. P.S. The /proc/mdstat file currently contains the following: Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md1 : active raid5 sdb[5] sdd[0] sdc[1] sdf[2](F) sde[4] 7814051840 blocks super 1.2 level 5, 512k (HowTos)