Are md0_raid1 and md0_resync doing vast I/O normal?

[Tom Horsley]

I setup a software raid on a couple of 4TB sata drives
not too long ago, and this morning I find md0_raid1
using about 10% of the CPU and having accumulated
about an hour of CPU time and md0_resync at about
half that, and gkrellm shows disks reads going at
about 180M (whatever units that happens to be :-).

Is this normal stuff for a software raid, or should
I be trying to find out what the heck is going on?