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I have a lot of data (about 7 TB), stored across multiple hard-drives with varying sizes. I would like to have a backup of that data to be safe against drive failure. A RAID is not a good option for me, as I want to keep my cost low and be able to easily extend the storage capacity of my setup by buying an additional HD.

I remember seeing a piece of software that generates parity data over all drives and stores that on an extra drive. That solution protects the setup from hard drive failure and works with varying drive sizes (as long as the parity drive is the biggest one).

But I can’t seem to find that software again. Does anybody now what I’m talking about or have any other solution for my situation?

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Raid5/6 is probably the most cost effective method when trying to maximize redundancy and effective available storage. However, if you're worried about performance then you will want to get a hardware RAID controller instead of using a software Raid Controller. Sorry that this refers to a solution that you were trying to avoid, but would be the direction that I would go. Raid6 will provide a double fault tolerance. 5x4TB Drives will give 12TB of space and 3x read speeds and 1x write speeds. –  kobaltz Oct 7 '12 at 21:11
I already own 3 2TB and 2 1.5TB Disks that I want to make part of this setup. I do not want to setup a raid 5/6, because they are by far not flexible enough (unless I’m missing something). I do not care that much about performance btw. –  Chronial Oct 7 '12 at 21:54
With those drives, you would be looking at a RAID5 with a 5 disk set. This would provide an effective available space (prior to format) of 6TB. It would only be 6TB because the smallest drive will be the max of each drive. I would start with something like this and an 8 bay tower. You can add drives and you purchase them. Add them to the RAID Array and it will increase your available space. This will provide more redundancy and efficiency than juggling what data is on which disk. 4TB drives are much cheaper now. –  kobaltz Oct 7 '12 at 22:12
If you're familiar with BSD, you should look at FreeNAS, I use it with iSCSI targets on my private cloud. It is an easy way to efficiently add new drives to a raid array. Windows 7 can be configured to point to the iSCSI target and mount it like a normal attached drive. Getting a smart switch and dual NICs bonded will ensure maximum throughput to the FreeNAS. –  kobaltz Oct 7 '12 at 22:16

1 Answer 1

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After 3 more hours of running the google, I found it again: http://snapraid.sourceforge.net/

Alternatives: http://www.flexraid.com/, http://www.vilett.com/disParity/

Why I was looking for a tool like that:

DisParity is a free backup utility that calculates parity from data on multiple hard drives. If one of the drives fails, disParity can use the previously calculated parity data, in combination with the remaining drives, to recover the contents of the lost drive. It's a fast, free and easy way to protect yourself against data loss caused by hard drive failures on home media servers.

The concept is similar to RAID, but no specialized hardware is required. Unlike traditional hardware RAID solutions, there is no limit on the number of drives that can be protected, and no requirement that all drives be the same size, or even on the same PC. The approach used by disParity is sometimes referred to as "software RAID" or "snapshot RAID", because the utility operates on a fixed snapshot of the hard drive data taken at a particular time. Because of this, it is not suitable for use on drives where files are changing frequently, such as database servers. It is perfect, however, for applications such as multi-terabyte home media servers, where files change infrequently.

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