For disks that I buy for use with Windows, my usual practice is to perform a long format before using them for the first time. A long format causes Windows to read and write every sector on the disk. When I did this with a 3TB disk, it took approximately 2 days.Now. Who know the procedure for testing disk?
If I subsequently need to reformat, I then do a quick format (unless I have reason to believe that the disk has developed a problem). A quick format merely re-initialises the file allocation table and other file-system structures, and so takes only a few minutes (even for a 3TB disk).
However, I did not do that for the disks that I installed in my NAS. The Synology operating system has some facility to "validate" a disk before it is used for the first time. I don't know quite what it does (it may be the same as a Windows long format). I chose the option to perform this validation when I setup my NAS, and the four 6TB disks took about 2 days to validate.
"Validate" is not the term that Synology use for this disk testing, but I cannot remember what they call it. There is also something called "data scrubbing"; I don't know whether that is the same as the initial validation, or something different. Your DS1512+ probably has the same facilities as my DS1515+.
-- from CyberSimian in the UK