A backup is where one has a second instance of there data. This second instance could be on the same hard disk as the original, or onto a completely separate disk. For example, one may backup their documents to a second folder, or a second partition, on the same drive as the original. This is still a form of backup. Is it a good form of backup? No. No it's not. Why? Because if that hard disk should fail you stand to lose your original, as well as your backup - everything. Gone. How can we solve this? We backup to a different HDD, or a different media, to the original source. Ideally you would backup your data onto a separate drive, be it an external hard drive, or onto tapes via a tape drive. You could even backup onto a second hard drive within the same machine if you wanted - it would at least cover you from your source HDD failing. With each of these solutions we would be able to restore our source disk and retrieve our data. More and more households are moving towards centralised data storage. This in itself opens many new doors and opportunities. We have those who use their storage devices, such as NAS boxes, as a centralised backup medium. All computers/laptops in the household would be backed up to that NAS/server. In the event of a system failure, data would be secure and could be retrieved. On the other hand, we have those who store all their movies, music, documents, precious photos, and so on, onto their NAS boxes so that all data can be accessed by all clients who are granted permission to access the resources - be it locally, or remotely. Since many of these NAS units, such as those from QNAP or Synology, incorporate RAID arrays, the data is completely protected should the system fail, right? WRONG. There are too many people on these forums who choose a NAS unit with the thought of complete data safety. Don't get me wrong, RAID is a great concept. You choose a level of RAID to suit your needs. Need the fastest access possible? Stripe. Need a duplicate of your data? Mirror. Want a mix of both? RAID5. RAID 5. That's the big one. That's the one everyone is after. That's the one that keeps your data safe, right? Again, wrong. So you buy your NAS. You buy your 3+ HDDs so you can set up a RAID 5 array. You put all your data onto the NAS and relax, knowing your data is safe. But it's not. RAID 5 is fault tolerant. Without getting into the workings of this level of RAID, it will allow a SINGLE disk in the array to fail. So that's one out of your 5 HDDs that can fail, and you can relax knowing your data is still there. You still have access to it. You can still use the NAS as normal. You replace that single disk and the array rebuilds, and you are back to where you started. Great, huh? Now let's say you have a major power outage and the NAS is abruptly switched off with no battery backup (UPS). You switch the NAS back on to find 2 or more disks have failed. Worse still, the NAS won't even power up. What now? Has the super duper RAID5 array saved you now? No it hasn't. BECAUSE RAID 5 IS NOT A COMPLETE BACKUP IN ITSELF! All your data. Them precious photos. The memories. GONE. If you use the NAS as a means to backup the data on your main computer then you can rest knowing you still have the main source of your data safely on your PC. If, like me, the NAS is your data source, then you're in trouble! Hopefully I have proven my point here and have shown you that although it's a great concept and it's use is encouraged, its not a fail safe solution. Although most disk failures do not usually occur in 2's or more, it's usually a single disk at a time, it can still happen. And we've seen it happen through many members here in this very forum. So what should we do? Most NAS units have either USB or eSATA ports in the rear of the unit. These can be used as storage expansion or as a means to backup. You could even purchase a second NAS to backup the first! Simply add a drive to your NAS locally, and your NAS will be able to backup your important data straight to it. Hence we create a copy of the data on our NAS to a separate external unit. . Is this enough? For most, it is. But what if, God forbid, your house burns down in a fire? That's still all your data gone. Hence we need to store an OFFSITE copy of our data. An offsite backup. Take your backup disk, the backup of your NAS, and store it at your parents house, at work, in the garden shed, at a friends - anywhere that's away from the main data source. Why stop there? Create more backups! I personally have all my data stored on my NAS. I regard my most important data to be my documents, my photos, and my home videos. Movies can always be redone or repurchased. Hence my important data is backed up to a separate external drive that sits right next to my NAS. Should I lose any data, or should my NAS fail, I still have all my data ready to be restored. But wait, that's not enough is it? I just said it sits next to my NAS! Therefore I have ANOTHER backup disc with another copy of the backup, which stays in my desk at work! Covered from all angles (unless both places burn down simultaneously, which is unlikely, right?)!! I cannot stress enough. RAID is NOT a backup solution. THINK. Just spend that little bit extra on a backup drive and cover yourself from any unfortunate situations! NOTE: I've written the above while hunched over my iPad. My back is hurting. I may have made several typos, and for that I apologise in advance. But if I have encouraged at least 1 person to get that backup drive and do the right thing, it will have been worth it! Right, now off to straighten my back!