* i think a raid 1 can only be built on two drives (not 100% sure about this)
According to specs, RAID-1 can be built on any even number of drives, (ie: 2, 4, 6, 8, etc). As long as there is always 1 source drive and 1 mirror drive, it will work properly. So you should be able to build a 2x2 RAID-1 array on the 5200, and have 1 extra drive in the system as a "hot spare".
I suppose it would be safe, but personally, I'd think that a RAID-6 would be more efficient and still allow for 2 drives to fail before being in danger of losing data.
please suggest where to buy trays for n5200.
i hope to use it as a form of back up solution. anyone comments on this?
I think you'll need to buy trays directly from Thecus.
As far as using it as a backup solution, I think it would work wonderfully. I use mine as a RAID-5 backup, and have it back-up computers over my network nightly. There were some issues with earlier firmware, but on the version I'm running (.08), it's pretty much rock solid (up-time of 1 month right now, with no issues).