Raid 5 vs raid 1

[Murphdy]

If I am using three 2Tb sata drives in raid 5 what is my overall capacity?

 

[sminlal]

In RAID-5 the equivalent of one disk out of however many you have in a set is used for parity information. The parity blocks aren't really all on the same drive - they're actually interleaved across all of the drives. But the space they use is equivalent to the space of one drive.

So with a RAID-5 set of three 2TB drives you're using 2TB for parity and you have 4TB available for data.

 

[Murphdy]

Thanks - I think I understand. Would using 2 2Tb drives raid 1 be more effective as back up system?

 

[cuecuemore]

Check out the table a couple screens down on this page for a good comparison of speeds and redundancies:
http://en.wikipedia.org/wiki/RAID

 

[Branden]

with 3x 2TB drives:
RAID 5 will give you 4TB space, and fault tolerance for 1 drive failure.
RAID 1 will give you 2TB space, and fault tolerance for 2 drive failures.

depending on the controller, both RAID 1 and 5 will likely have comparable write speeds, but RAID 5 will probably have significantly better read speeds over RAID 1.

 

[sminlal]

Thanks - I think I understand. Would using 2 2Tb drives raid 1 be more effective as back up system?

See the above posts with respect to the capacity of RAID 1.

But you should understand that RAID is a lousy way to do backup. Redundant RAID configurations protect you from drive failures, but that's far from the only way you can loose data. RAID won't protect you if you accidentally delete a file, if your drive gets corrupted or hit by a virus, if your system is stolen, if you knock over the computer and damage both drives, if a power hit fries your system, etc. etc. etc.

If your data is important to you then you should use at least one of those drives for true backup, where the files are copied to the disk and then the disk is disconnected from the computer and stored separately. The very best backup strategies keep at least two offline copies of your data with at least one of them stored offsite.

 

[g00ey]

The backup thing is easier said than done. I mean, what medium should be used? If you have say 5-10TB of data to backup then there are not many reliable options if you can't afford a modern LTO solution..

 

[sminlal]

The key with backup is to organize your data to reduce the frequency with which you need to back up files. If you have 10TB of data then chances are the vast majority of it never changes and doesn't need to be backed up every month. And if that 10TB of data happens to be something like, say, ripped DVDs, then the need for backup is questionable since you can always go back and get the movie from the original source anyway.

IMHO the cheapest and most convenient backup media is hard drives. They allow for very large backups and can easily be scanned for readability. IMHO tape-based backup technology is nearing the end of its usefulness, and is already obsolete for personal use.