I bought 2x Samsung F3 EcoGreen 2TB hard disks to make a backup storage. I put them in Raid 1 (mirror) mode. Made a single partition and formatted it to NTFS, running Windows 7.

For some reason, accessing the drive's contents (simply by navigating folders) is sometimes really slow. Like opening D:/photos/ can sometimes take several seconds before it starts showing any of the folder's contents. Same applies for other folders.

What could be causing this and what could I do to improve the performance?

I remember that there was an option somewhere inside Windows to choose fast access but less reliable persistence operations (read/write). It was a tick inside some dialog. At the time, it felt like a good idea to take the tick away from the option and get more reliable persistence but slower access, but now I'm regretting. I'm unable to find this dialog.. I've looked hard. I don't know, if it would make any difference.

Oh, and I've ran scan disk and defrag on the drive. No errors and speed isn't improved.