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I've done lots of reading up on the topic of RAID but still can't make a fully informed decision on the best solution for me!

I have a new external hard drive dock that takes up to four drives, I have two identical 1TB drives, one other 1TB drive and a 750GB drive.

I am looking to use this box for storing all my important data (such as photos) so needs to have a fault tolerance of a minimum of one!

The box supports

  • BIG (Spanning or Concatenation) - No fault tolerance
  • RAID 0 (Striped Disks)
  • RAID 1 (Mirrored Disks)
  • RAID 10 (1+0; Striped set of Mirrored Subset)
  • RAID 3 (Striped set with Dedicated Parity)
  • RAID 5 (Striped Disks with Parity)

What do you think is the best? Obviously the more storage available the better, and the more speed the better and the more fault tolerance the better. Which is more important? It is an external Firewire drive, so I am thinking the speed is going to be limited by this anyway?

Many thanks!

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4 Answers 4

up vote 6 down vote accepted

RAID is NOT about keeping your data safe!

RAID is about keeping the data accessible all the time even if something goes wrong. Do you really need to be able to access your data all the time?

Use one of your disks as a backup-destination (using rsync or some other solution) if you want to keep your data safe.

Remember that:

The whole purpose of a RAID is to make sure that nothing in the world can interrupt that accidental rm -rf / (or DELTREE /X C:), not even yanking the power chord in panic.

(source of above quote)

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1  
Isn't RAID about making your storage redundant? ... "Even if something goes wrong" is kinda incorrect-If there was corruption or an accidental file deletion on one side of the RAID 1, it'll go onto the other too. –  JFW Sep 26 '10 at 13:02
    
@JFW - A RAID would pick upp a corrupt file (filesystem level corruption) but would happily allow an accidental deletion. –  Nifle Sep 26 '10 at 13:05

RAID5 is typically used for redundancy. So, if one drive fails, your data is still there. There are some speed benefits as well. RAID5 is also more common for servers than desktops.

RAID 1 is not a reliable backup option. If one drive fails or the data gets corrupted, it sometimes gets carried over to the second drive. I've seen this first-hand more than a few times.

RAID3 and RAID10 don't offer enough redundancy to always survive a failed HDD.

RAID 0 offers performance, but doubles your changes of data loss since if either drive in the array dies, you loose everything.

The best option would probably to use one drive as your O/S and programs, another for data, and a third for external backup.

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Without them all being the same size, you may have a bit of trouble.

Personally, I would use Raid 1 if backup is more important to you, Raid 5 if space is more important.

However, just remember RAID IS NOT BACKUP

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RAID 1 & 10 are typically used for speed. The down side is you use half of your storage for fault tolerance. RAID 3 is so uncommon I would avoid because if you needed to find a replacement machine to read that could be a pain. RAID 5 & 6 are more common and widely used. They allow for the most fault tolerant space in that only 1 or 2 (RAID 5 & 6) are needed for parity information. RAID 5 you need a minimum of three drives. RAID 6 I typically see with five drives.

Also, if the files are large, I believe you will get better transfer speed with firewire than USB.

One more thing to consider is getting a controller or OS that allows you to use the drives fully. For example you have three 1TB drives and 1 750GB drives. Some controllers/OSs allow you to use 750GB across all four drives and then make a second RAID across the remaining three drive's 250GB. Otherwise you would loose 750GB of space.

As a side know I've heard many photo people speak their love for Drobo, many love the Drobo S because you can have five drives and it has eSATA. If you wanted an out of the box solution (and had the money), this may be a good fit for you.

I also agree with everyone talking about backups. Hard drive fault tolerance isn't a replacement for backup, but I don't believe that was in your question.

(I almost forgot, for all the ZFS lovers out there. ZFS have similar fault tolerance measure to RAID 5 & 6 call RAIDz and RAIDz2. I love ZFS because you can ensure the entegrety of the data and it had compression and deduplication. ZFS is available on OpenSolaris (no longer development), OpenIndiana (formed to continue OpenSolaris), FreeBSD, and Linux (via fuse and soon baked into the kernal).

FreeNAS is a great white box NAS software for RAID, iSCSI and the like, plus it is easy to setup. FreeNAS had ZFS as well, but the advanced versions of ZFS hadn't hit FreeNAS as of yet.

I also forgot to mention that ZFS does have a Mirror configuration.

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RAID 1 is not used for speed, RAID 0 (striping) offers the most speed, but increases risk of failure. RAID 1 is much slower, and is usually actually slower than a single drive, because it writes the same data to both drives. –  TuxRug Sep 27 '10 at 1:45
    
A case can be make of any RAID is better over the other depending on number of disks, hardware/software RAID. Ultimately, the type of RAID have trade offs depending on your needs and hardware. Unfortunately, RAID 0 despite its performance benefit was excluded because no fault tolerance. That is why I didn't include RAID 0 in my answer. RAID 1 can have the benefit of 2x read speed but only a 1x write speed. Because there is no parity to calculate RAID 0 could be faster. (depends on hardware/software, and the number of disks) –  Scott McClenning Sep 27 '10 at 4:20

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