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My external HDD died and I've lost everything, so I've decided to spend some money to prevent future loss of my critical files.

I want to buy a NAS with 4 or 5 bays, with 2 disk redundancy. I already chose the disks, the famous WD RED 3TB.

The main use will be as my home central storage (for my PC/tablet and my girlfriend laptop), and as repository of all my movies.

My questions are:

  1. Can the media center, accessing directly the NAS shares could cause any integrity problem? I want to use the NAS as a XBMC repository.
  2. If I buy a 5 bay NAS, can I use 4 disks with RAID 6 for storage and 1 disk individually to run some services, like web server, ftp, ...? Would it be a good idea?

Thanks in advance

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My questions are:

Can the media center, accessing directly the NAS shares cause any integrity problems?

No. A NAS should be able to deal with that.

(A SAN which an directly exported block device and the wrong filesystem on it might not, but a NAS operates at a different level and should be fine)

If I buy a 5 bay NAS, can I use 4 disks with RAID 6 for storage and 1 disk individually to run some services, like web server, FTP, ...?

You can.

Would it be a good idea?

No. First because using a four drive RAID 6 array is wasteful. You only get the storage space worth of two disks from four drives. RAID 10 is also quite safe, offers the almost the same protection (1 or 2 disk failure, depending on which disks fail) and is a lot faster.

Secondly because you do want an external [off-line] backup.

Even two spare disk in the NAS are not going to rescue you data if there is a fire, if lightning hits or if a thief steals your equipment. The only truly safe solution is to have a second backup at a different location.

Thus I would not use 4 disk in RAID 6. Either use 3 disk in RAID 5, or 4 disk in RAID 5 to get more storage space, or 4 disk in RAID 10. In all cases make an external backup (e.g. a simple yearly copy to a disk which you then store somewhere else. Or a cloud based solution where you rsync the changed data to a different place.)

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Thank you Hennes. I was planning to have and external HDD and backup the most critical files weakly to it. So, the best choice would be 4 disks in RAID 10 instead of RAID 6? – CSeven Jun 15 '13 at 14:30
RAID 5 and RAID 6 can suffer from a write hole. This is why most people only use them when you want some protection but can not afford to loose a lot of disk space. (e.g. it makes a lot of sense on a file server which automatically warns the network administrator that a disk has failed. That admin keeps the server up during the day to the people can do their work, and then at 5 PM he replaces the broken disk and rebuilds the array). It also is fine in a home environment where you just do a lot of reads but not many small writes. It is however not build for maximum safety. – Hennes Jun 15 '13 at 14:36
For maximum safety consider mirrors (E.g. RAID 1, loose half the disks), a striped mirror (RAID 10), or even two two-disk RAID 1's. The latter even has the advantage that you could dump all move on one array, the rest on the other array and keep one set of drives spun down until you need them. (e.g. use hdparm -S NUMBER to set standby mode on the drives after some time with no activity). – Hennes Jun 15 '13 at 14:40

In your case, rather than buying a NAS, I would recommend to build an HTPC/NAS directly, and install XBMC on it. It would cost you less and you could do more.

For example, you can buy a Mini ITX Motherboard with 5-6 SATA connector, then a NAS enclosure for your Mini ITX motherboard with 4 Hotswap drives and one internal hard drive ( such as : ), and use then the internal hard drive for your system, where you install XBMC, Web Server, FTP, ... and the 4 Hot swappable hard drives for your data.

If you want to have maximum security, you can even (with a bit of DIY) put two 2.5" internal hard drives and run your system harddrives in RAID 1.

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