Ra_V_en :
kanewolf :
You could replace it with a new server if you are using a windows domain. If you are only using a workgroup, then you could replace it with a NAS.
Not sure where did you get those conclusions from, almost any small-office grade NAS will have no problem with sharing over AD... even $200 WD My Cloud EX2 does.
I totally don't agree which a multiple lan ports or requirement of the managed switch, the fact is if the switch he has is already 1Gbps it's far more then fine within a 10 station network. If you don't have a RAID 0 or 10 configuration the hard drive attached to it will already hit its limits especially on smaller files.
Making backup of hdd on another hdd is just what raid 1 does... if you want more then you choose different media type for offline backups like streamer or BD.
May personal type for OP needs would be something at grade of Synology DiskStation DS412+ or WD My Cloud EX4.
My point wasn't that a NAS and AD were incompatible, it was more "maybe you need a new windows 2012 server" ...
If this is a domain server in addition to a file server then a NAS is not the optimum solution.
But for $1200 what I would recommend is a
DS415+, 4 2TB
WD Red disks. Create 2 RAID 1 volumes. Allocate your storage needs across the two volumes and have them back each other up. Also I would get a managed switch such as
this to allow you to use link aggregation with the NAS.
You will end up with 2 TB of RAID 1 with full backup.
I am sure that somebody will have a Qnap or Thecus version which is similar.