a couple of months ago I've created my first htpc, witch is working perfectly, but after a couple of months I realize that I need to improve the storage.
right now I'm having 5 sata hd, 1.5gb each one.
but since my focus is downloading blu-ray movies, and the average file is 8-12 gb I'll be needing more storage space on the next months.
So, put them on the case make non sense, for space, temperature, weight, etc.
I've been checking some nas solutions but I'm not sure if this is the correct path to go, what do you expert suggest?
I'm looking for a scalable, fast and no too noisy solution.
usually the process is this: I download on one disk, process over there (unrar, check quality) and if everything goes right I've moved to the drive and then upload it to the home theater db. Also I use it for tv series.
Looks like you are downloading Blu-Ray movies encoded to MKV files since actual BL movies are typically 25GB - 50GB depending on if the movies is stored on a single layer or dual layer BL disc.
It seems you are doing the correct thing... downloading to one hard drive before moving over to a different hard drive for storage. That means wear and tear is mostly confined to one drive so if it dies, then technically speaking it should not have too much data on it.
Regarding your issue, a NAS is the best solution since you have a single point of failure; the hard drives in your HTPC. I have a similar set up as you do but with just 4 1TB hard drives to store media, they are in a RAID 1 configuration so effectively I only have 2TB of storage. I have a seperate drive for the OS and another drive (I call it my "Thrash Drive") to rip DVDs (haven't switched over to Blu-Rays yet) and do the occasional download.
I don't have a NAS, my apartment is too small for that. But a NAS is probably the best option for you to serve as a backup. If you are simply looking to add capacity then you can still go with a NAS, but you are going to run into a problem in the long term... you have no backup solution.
If you are simply using the NAS as additional storage and you do not burn your movies onto blank discs, then you are back to the single point of failure issue. Unless you have additional NAS to backup your HTPC and your "storage NAS".
If you are filling up 7.5GB of storage space every 6 months or so, then you have to...
1. eventually delete some content you don't want anymore.
2. backup the content onto blank discs then delete.
3. Build yourself a server farm so that you can continually add 7.5GB of content every 6 or so months as well as backing everything up.