Storage Capacity Sacrificed in Various RAID Systems?

[kn]

I'm slowly converting my media library to digital format and have quickly run out of space on my 3TB drive. I plan to continue adding over the years and want some sort of safeguard against catastrophic failure.

I'm trying to understand the various RAID systems. RAID 0 is a no-go but since this isn't mission critical, I think I can live with RAID 1. From what I've read, this means I lose half of the storage capacity, correct? Isn't this true of RAID 5 as well?

For example, the following storage system comes pre-configured as RAID 5. How much actual storage space is there as a result?

http://store.apple.com/ca/product/HE...fs=s%3DpriceHL

I don't care about write performance as once a movie on disk, it will only ever be read.

I'm using the Apple ecosystem but that shouldn't matter for this situation from my understanding. I'm open to cheaper and alternative solutions but would prefer dealing with fewer drives. I did read Dell not recommending RAID 5 on drives larger than 1TB but don't really understand why.

Thanks.

[nik-]

RAID 5 will get better as you increase. 33% capacity loss with three disks, 25% with 4, 20% with 5.

http://www.raid-calculator.com/default.aspx

[kn]

Originally Posted by nik-

RAID 5 will get better as you increase. 33% capacity loss with three disks, 25% with 4, 20% with 5.

http://www.raid-calculator.com/default.aspx

Awesome! Thanks... didn't think of searching for a RAID calculator.

[photon]

Originally Posted by kn

I plan to continue adding over the years and want some sort of safeguard against catastrophic failure.

Keep in mind RAID isn't backup.

The only failure RAID protects against is disk failure, it doesn't help with any other kind of catastrophic failure. It doesn't protect against human error, file corruption, fire/flood, multiple disk failures (not unheard of), UREs (that can really wreck your day when you're rebuilding an array)...

If it's media that you can re-convert later, then depending on RAID (RAID6 is safer than RAID5) might be acceptable, but having a way to backup offsite if re-converting isn't desirable or feasible is a good idea.

[FlamingLonghorn]

Originally Posted by kn

I'm slowly converting my media library to digital format and have quickly run out of space on my 3TB drive. I plan to continue adding over the years and want some sort of safeguard against catastrophic failure.

I'm trying to understand the various RAID systems. RAID 0 is a no-go but since this isn't mission critical, I think I can live with RAID 1. From what I've read, this means I lose half of the storage capacity, correct? Isn't this true of RAID 5 as well?

For example, the following storage system comes pre-configured as RAID 5. How much actual storage space is there as a result?

http://store.apple.com/ca/product/HE...fs=s%3DpriceHL

I don't care about write performance as once a movie on disk, it will only ever be read.

I'm using the Apple ecosystem but that shouldn't matter for this situation from my understanding. I'm open to cheaper and alternative solutions but would prefer dealing with fewer drives. I did read Dell not recommending RAID 5 on drives larger than 1TB but don't really understand why.

Thanks.

The reason Dell doesn't recommend Raid 5 on large drives is because drive rebuild times are so long on drives larger than 1 TB (7k speed) that the chance for a second failure is too large to risk it. This also assumes you have a hot spare hard drive waiting to be built in place of a failed hard drive. Raid 6 takes up 2 drives worth of capacity for redundancy so it can stand 2 failures. Raid 5 can stand a single drive failure. This recommendation is based on business class/enterprise class storage. For your home you have to determine your own risk. If you are also backing up the data elsewhere than I would go ahead and do Raid 5 as you aren't losing revenue like a business if your main storage is down. If you aren't backing up the data (I would), you might want to do a raid 6 with a spare (if your storage supports this).

[-TC-]

for a home user, cloud based backups make more sense than RAID.

it's already been explained why so I won't get into it, but it seems to me that buying/building an array that supports RAID5/6 for a home users music and movies seems to be overkill, especially when it's not really a backup in the truest sense.