Any good NAS can lead to a bad oversight. That oversight is the feeling that your data is safe and doesn't need a backup. (RAID 5 helps but even without it, you feel somewhat safe knowing your NAS is a few floors down in the basement...you might not hear grinding from the drives (lol...yikes)) Having such a huge NAS, in my case, I am really not able to back everything up nor do I need to. I will just break down some of the common categories and my feelings on them so everyone reading this can also reevaluate their own solution:
1) Music. Ranging from small to large collections, lossy libraries are not usually more than 50-200 GB. Lossless libraries are likely to be smaller because you often can't just download lossless files. However, the files are also substantially larger (5 times?) In that case, I fall at around 300 GB so we'll say 200-500 GB for a lossless collection. In any event, this can be a large data set but it also requires the most work to restore. That library would consist of 500-2,000 CDs or so. Each one taking 5-15 minutes! Now you're talking a month to restore in free time. This really should be backed up. It is great to backup to two locations but that may be tough. If you're on a lossy library, burning to DVD is a great option, taking 10-40 DVDs. It would be handy to find an indexing program that would allow you to incrementally add files to more DVDs without backing things up twice.
2) Photos. Now here, your data set could range quite similarly with the music section. Depending on your habits and efforts to digitize analog photos, you could easy compile a few hundred GB's. I personally am under 50 GB now but have 30,000 analog pictures/slides/etc I need to scan in which could easily add 200 GB to that number. Compared to music, which could take a month to restore, I don't even want to consider how long it would take to restore this collection, assuming it's personal photos. Therefore, you absolutely MUST have two complete backups (plus an online media) and ideally, a burnt media. I always consider the change that some huge magnetic eruption from the earth or solar system could destroy all our hard drive data so another type of media is a great option here. I'm thinking most collections are under 50 GB, too, so DVD backup wouldn't be that challenging. How does flickr or other online photo services assist in this area? I'm interested in feedback regarding free online "original file" backups. It wouldn't be terrible to have a lower res backup as a last resort, though!
3) Video. Lots of people probably have at least some home movies and I'm guessing their burnt to DVD already. I personally have around 100 DVDs of personal home movies ranging from my beginnings on this planet to our modern activities, etc. I have an A and B set of DVDs I keep in two identical binders. I will consider creating a third, C, set in a few years since DVDs may "die" over the years. I also keep these on my NAS. In general, I don't need to back these up again because I already have two DVD copies (one I usually keep offsite) and I have two onsite copies. At around 360 GB for all 100 DVDs, this is quite similar to my music collection or what I think my photo collection will be in a few years...it can't all be backed up amazingly. Besides, burning these movies to DVD just makes sense. That's how most people would watch them. I prefer the computer with MC or VLC but it's still just a perfect, modern format.
4) DVDs. These really don't need to be backed up a second time nor can you afford to back them up again! One backup to a NAS is enough. In the worst case, these could theoretically be replaced. Also, re-ripping them would be much more reasonable. At 100 TV DVDs, & 100 movie DVDs (excluding 100 home DVDs), this comes in at around 1,200 GB. That's way too much to try to backup. They also take around the same time per disc not to mention the fact that I have 1/5 as many DVDs compared to CDs, so the recovery time is greatly reduced.
5) Installers. I keep copies of all my installers and purchased software as backups with the purchased licenses. These only account for 10 GB so might as well back them up! Don't really want to lose all the licenses for the software I've purchased!
6) Podcasts. They really aren't worth it! In the worst case, it would force me to clean out my folder...lol. I usually accumulate tons of files that I wouldn't ever have time to listen to...although I only subscribe to a limited number of podcasts: CrankyGeeks, dltv, hak5, happy tree friends, indigital, radio leo, tikibartv::: but they still pile up and just get in the way. I, at one point, deleted 30 GB of podcasts. At that point I was subscribing to 2-3 times as many, though.
7) Documents, Profiles. I keep all my families documents (4 users) plus some shared documents folders in a Documents folder and a Profiles folder which contains our Desktop files, firefox profile, media center database, screensaver pics (for screensaver), sunbird profile, temp (MC rip), thunderbird profile, and wallpaper pics (for background). As a side note, I highly recommend the free Auto Wallpaper Changer. I install it on all our computers and I have a registry file I custom crafted so when I double click it, it automatically sets that computer's user account up with my custom settings and points it to my NAS wallpaper folder. That way, all our computers draw from one folder and get a new background every 30 minutes. I can keep the wallpaper fresh and relative to events of the time. I also have a screensaver folder but don't use that as much. I'm thinking I'll disable the screensaver altogether on my next format. Anyway, this amounts to under 20GB and is obviously VERY important. It has all our favorites, documents, profiles, address books, calendars, some pictures, etc. It's really all the stuff we use on a daily basis whether it's just the background, opening firefox, etc. These things can be recreated periodically as a way to help clean out things but you definitely don't want to lose the core data. Back this up a few times! It's small and easy.
Web Site. If you mess around with a web server or make sites for fun or professionally, obviously back them up. Don't forget the databases and email database if you run an email server. (I recommend the free hmailserver--very easy to use).
Any other major categories we should consider? I just thought it would be good to discuss backing up in a bit more detail, so let's hear the discussion roar!