OK. This is very weird. A few months ago, I had some trouble with one of my external RAID5 arrays, so I reinitialized and rebuilt the array. Before I rebuilt it, I was able to copy to it using Multi Commander at normal speed (about 80MB/s), but afterwards, the copy is very slow (about 2.5MB/s). The really weird part is this slow copy ONLY happens when I copy from one drive. If I copy from any other drive to this array, the copy runs at normal speed.
Slow copy screen shot:
https://imgur.com/jIIygCzCopy from the same source drive to the same destination drive using File Explorer:
https://imgur.com/cSn4C2BIf I copy in Multi Commander using that same source drive (D:) to a different destination drive, that copy runs at full speed. If I copy from that other drive to this destination (U:), it runs at full speed. ONLY when I copy from D: to U: in Multi Commander do I get this slow speed.