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I can't understand the logic behind RAID

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ZachiusMaximus

New Member
Joined
Jan 10, 2010
Okay,
My friend wants to set up an htpc for blu ray rips. It seems that every guide recommends a RAID setup, which from my basic understanding means that the movie is split up to two or more harddrives. But what is the point of doing this?

Let's say that you have all your movies spread across two harddrives, and one harddrive inevitably fails, then you lose all your movies. Whereas if you put individual full movies on one harddrive with no RAID setup, and one harddrive inevitably fails, you only lose half of your movies.

I understand that RAID allows for faster access times, but isn't a single harddrive fast enough to play a blu-ray movie?

Even if you wanted to go big with twenty 1 TB harddrives, it just seems to me that the hands down best way is no RAID setup so when a harddrive fails you minimize loss.

I'm sure somebody out there can clear this up for me.
 
Striped RAID is for speed, and yes, if one drive dies you're screwed. Most people back up though, or use mirrored RAID or RAID 5. Lets say you had three 1 TB drives in RAID 5. You would have about 2 TB of usable space, any one drive could die without data loss.
 
I've read the Wikipedia article, that's the first place I go for just about everything haha.

In regards to your comment about mirrored RAID or RAID 5... okay you have 2 TB of movies, how could you possibly back up 2TB of movies into 1 TB. It seems to me that 2 TB of movies would have to be backed up to 2 TB....get what I'm saying?
 
Research "Parity" - That is the way RAID-5 (and 6) works...

Even RAID-5 or 6 is NOT a substitute for secondary backups!!!

:cool:
 
I'm not really the person to ask about this, but as I understand it you run a RAID 5 with 33% overhead... so you only need 1/3 of your total space to use as a backup. But in a case of more than three drives, still only one is the spare... (this is the part where you can see I don't quite know what I'm talking about :D) But you always only can use 66% of a RAID 5 array in actual storage, and only one drive can fail before data loss.
 
It is 33% with a 3-Drive RAID-5 array. Basically, the Parity in a RAID-5 array eats up one drive's worth of storage (but spread across all 3 drives) - so in an 8-drive RAID-5 you only "Loose" 12.5% storage. EVERY drive stores parity information, and basically Parity allows the Controller to re-construct the missing data on a single drive. RAID-6 uses 2 instances of Parity to allow 2 drives to fail, but also eats up 2 drives wrth of storage.

Basicaly, it is like a+b+c=x (x is parity). If drive "a" is lost, then ?+b+c=x and the result is easily determined for the "Rebuild" of drive "a". A simular set of Parity is derived if drive b or c fails instead. Something like that...

:cool:
 
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So if I wanted to forgo the whole RAID thing, put entire movies on one drive, and when that drive fails just buy a new drive and re-rip the movies....there would be no problem in doing it this way right?
 
Of course - but consider how long it takes to re-rip (re-encode) 1000GB's of movies! (Probably weeks) RAID is not for everyone, but having a true backup of your data on a seperate drive is a must in my eyes.

RAID-5 (or RAID-6) is also not that difficult to setup, and once setup, it is ubiquitous. Once you get into multiple TB's of Data, RAID arrays make a lot of sense IMO...

:cool:
 
Here is what I do, 1 hdd in comp and 1 external drive (or use the external dock) for backup.
 
With raid5 when a disk fails you just put a new disk in and it rebuilds the data. So you don't have to re-rip/encode anything. The down side is it costs more because you lose a drive to parity plus you need a raid controller. Onboard works ok but a dedicated card is much better.

I run raid5 with a dedicated card (Perc 5/i) but if I were to do it again I think I would just build a cheap WHS machine. The price of the extra HDD + raid card is about the same as a cheap WHS. WHS has duplication so it can give you similar redundancy, but you can pick and choose which folders are duplicated. Plus all the other features of WHS.
 
Sounds like the OP thought that there was only 1 kind of RAID, which sounds an awful lot like RAID 0. I don't think anyone in their right mind would use RAID 0 in an HTPC. I'd rather just drop it out a 3rd floor window. ;)

That being said, I have all of my media on a large RAID 5 array on a 3ware 9650SE controller in a different PC. My HTPC just taps into my media over the network and just has a single 300GB drive that houses the OS and any temp DVR recordings I might want (which are few).
 
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