We just got it back up to fast speeds, but can't replicate it. Here are the things we did before realizing speeds were faster:
- Stopped Trend Micro antivirus; but, it was already set to not scan the drives being backed up from and to, and fast speeds have been achieved in the past with Trend Micro running, so this should not be the issue.
- Ejected one of the hard drives. A custom drive management application is used to eject the drive, which is provided by Idealstor, and its service was not running so we had to start the service, then launch the program, and then use the program's eject function.
- Replaced that hard drive into the same slot. (this was the left SATA drive on the 2-bay enclosure)
That's all that was done. We think it could be some anomaly that was magically fixed by pulling the drive out and putting it back in. But restarting the antivirus (and restarting the task) didn't slow the task, nor did stopping the management service and restarting the task, or exiting the management application and restarting the task. We could not slow the task back down, so we can't trace the cause.
Also just a note, it is not a temperature-related issue; the reason for pulling out the hard drive was to test its temperature, which was found to be a cool 27 C, even after the backup task had been running for an hour beforehand (albeit very slowly, as explained). The individual hard drive enclosures each have two small fans at the front of them, and our server closet has a constant cold airflow, so there is absolutely no chance that the drives or the controllers are overheating.