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| Ozzik: The beginners guide to HTPC, Part III. |
18-1-07 20:56:49 |
Now, let's talk about storage problems. Problems for some of us. Some people will watch a movie and then delete it. These people will also say that 250GB of space is way more than enough. These people can also skip this chapter, as they won't find anything interesting in here.
Myself, I belong to another category, you may call it the collectors category. I never delete anything, unless of course it's an absolute crap. People like me, we need a lot of space. I'm talking about terabytes. The problem is that having that much storage is very dangerous without a backup. And backing it all up on DVD's ain't real. Solution? RAID.
RAID (redundant array of independent disks) refers to a data storage scheme using multiple hard drives to share or replicate data among the drives. Depending on the configuration of the RAID (typically referred to as the RAID level), the benefit of RAID is to increase data integrity, fault-tolerance, throughput or capacity, compared to single drives.(wikipedia).
In other words, few hard drives brought together to store the data and back it up at the same time. Few important points:
1. The drives have to be the same capacity, otherwise they will be brought down to the capacity of the smallest one.
2. There are at least 10 levels of RAID that I know of, but what interests us are levels 1, 5 and 0+1.
3. Level 1: Two hard drives are mirrored, i.e. one drive is the actual drive, the other is the exact copy of the first. In case one of them goes down, you're automatically swithed to the second one. And the data is safe. When you replace the damaged drive, the RAID array will be automatically rebuilt. Nice solution, but demands twice as hard drives, thus twice as expensive.
4. Level 5: At least 3 hard drives, and you can add as many as you want.
There's a complicated formula of writing the data on all of the hard dives, which I cannot fully understand myself, but the bottom line is that it doesn't matter how many drives you have, it will always keep one as a reserve. That means, if you have 5 drives in RAID 5, you'll actually have the storage room for 4 drives, if you have 10 - you'll be left with 9 and etc. The beauty of it is that if one of the drives goes down - it will keep all the data, and of course safely rebuild itself when you replace the drive. Of course if 2 drives go down simultaneously - you're in deep shit, as you probably gonna loose all the data.
5. Level 0 is not of any interest to us, as it's very not safe, but a lot faster than any other RAID, I must say. It works like this: 2 or more drives are joined together as one logical drive. It gives the best performance, but is not really a RAID itself, since it's not fault-tolerant (data is not backed up in any way). This means that if one of the drives fails - you're loosing all the data at once.
The reason I'm mentioning it is because the RAID 0+1 is something much more interesting.
6. Level 0+1: This one consists of two RAID levels. It needs at least 4 drives, when two pairs are striped between them (RAID 0) and there's a mirror between the two pairs. That is the drives 1 and 2 are in RAID 0, as are the drives 3 and 4, but you only get the 2 drives storage room, as the other pair is just mirroring the first one. This is a very good and fast RAID, but the problem is that you loose the whole array if one of the disks goes down, although it's totally repairable. Of course it's also not a very cheap solution.
In conclusion we have that the cheapest and the most effective RAID level is 5, although not as fast as the others and on a risk of data loss when 2 drives go off at the same time.
Next important point is that you need a room for all of the hard drives. Let's say you can put 4 drives in 1 PC, but today the largest drive available is 500GB, that means that even if you make RAID 5 level, you'll still be left with 1400GB(not 1500, the drives are always smaller than they state). And even if in a couple of years there will be much larger drives available, the media files sizes are gonna grow as well, as the HD media is coming into the masses - you'll always be short on space.
So what can you do?
To tell you the truth, at this moment I have no real solution. One thing is for sure - it's gonna cost a lot. But you gotta pay for pleasure. Having your own free VOD service is not that cheap.
I'll just give you a couple of tips on what you can do in this situations.
You can buy(even on ebay) a large storage box or server case, put in a motherboard+CPU+memory+power supply+good RAID controller and put all of your disks in.
You can a buy a storage server - will cost a fortune, I guarantee you this much. You can also split it between few cheap boxes across your home local network. Might also be the safest solution, because in case a power supply decides to hit with over voltage - you'll not loose all the data, along with all the drives.
Of course the UPS is a must for a RAID PC/server and very much recommended for the HTPC itself(as for any PC really).
Sorry I can't provide you with a real good and relatively cheap solution, but it's just because there aren't any.
The last thing I wanted to mention is the RAID controller itself.
First of all, never make RAID in the operating system, whether it's Linux or windows or whatever. It's totally not safe.
Second of all, a lot of motherboards today come with an integrated RAID controller – be aware that it's not a hardware one. Although it is a chip, it doesn't have it's own CPU or memory on it, i.e. it uses the resources of the PC itself. Also there are a lot of relatively cheap controllers on the market with the same performance issues.
Wiser would be to buy a controller that does all the work by itself, although it costs twice as much. Remember that while reading off of level 5 RAID is pretty good, the writing is rather slow, but I'm assuming you won't be using it too much for writing, as it's more of a storage and not a data factory. Every now and then you copy some stuff on it and that's it.
Sorry about all this long article, but I thought you better read it now, before you go and buy yourself disk after disk after disk and at one point find out that you have no more room for drives, and when you finally decide on going for a RAID solution - you'll have 2 terabytes of unprotected data, that you won't know what to do with, as RAID will of course need first to reformat every drive you decide to join in.
But then again, don't take it too serious, unless you're absolutely certain your collection is gonna grow real fast and 3-4 500Gb drives seem pretty much like a space to begin with.
Next: Operating Systems and the actual Software for the HTPC function. |
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