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I have 8 HDD totaling 9TB, as detailed below:

  • 3 x 500 GB
  • 3 x 1 TB
  • 1 x 2 TB
  • 1 x 3 TB

I am looking for create a spanned volume of the 3 x 500 GB and the 3 x 1 TB (total 4.5 TB). Since a spanned volume is fail intolerant, I would like to backup this volume to the remaining drives (1 x 2 TB and 1 x 3 TB, totaling 5 TB)

I need a solution that can do automatic differential backup of the spanned volume and split it into the remaining drives. I could use a spanned volume here as well, but I would lose the backup if one of the drives fails.

I am trying to figure out the best use for all these drives without having to deal with 8 different volumes or lose all my data if one drive dies. RAID is out of the question because of the different sizes.

I'm running Windows 7 Ultimate x64

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  • Would something like Delta copy work or a you looking at building your own solution within windows?
    – 50-3
    Commented Sep 17, 2013 at 22:13
  • Are you actually looking to make Spans or are you actually trying to make Stripes (RAID-0)? Why not stripe both sets then use your favourite backup software to do differential backups to the 2nd stripe? Why do you think RAID is out of the question? Most decent RAID controllers can pull off mirroring two different sized sets; you'll get a mirror that's the size of the smallest set. (*RAID is not backup ;) ).
    – Ƭᴇcʜιᴇ007
    Commented Sep 17, 2013 at 22:45
  • @OP: 1) RAID does not inherently prevent you from using different sized disks (though you might have to get creative with partition sizes. 2) RAID-0 (stripe) does not just mean no redudancy. It means that loosing a single disk in the stripe will kill your stripe. 3) As techie said: RAID is not backup. You will need an off-line off-sitr backup. Or in simpler terms: Fire, thefts etc should not take out your backup. 4) +1 for delta copy on windows or rsync on anything else.
    – Hennes
    Commented Sep 17, 2013 at 22:48
  • I know raid can still be used, but it will either A) limit the capacity to the smallest drive in the array, or B) I will need to partition them and use multiple arrays to match the sizes... that is why i would rather spann them into a single volume instead of striping them. I think i will divide the drives into two 4,5TB spanned volumes and make them mirror eachother using a third party backup software like suggested... this will allow for one drive to fail in either of the volumes at any given time.
    – Daniel
    Commented Sep 18, 2013 at 3:10
  • I know you marked the post with windows 7, but I think you can actually do this with ZFS (which works on Solaris, FreeBSD and Linux). It might be worth keeping your eyes open for a port to windows.
    – Hennes
    Commented Sep 18, 2013 at 15:18

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As @Hennes said, RAID-0 (aka Striping) will ultimately kill your data if one drive would fail. Spanning, as defined here and here will also kill your data if one drive would fail.

From a practical point of view, they are the same. I'll use RAID-0 to refer to all this later on.

As Hennes also said, RAID is not backup; think of it more as fault safeguard (as if a drive were to die, stop working). You are correct in saying normal RAID modes demands drives to be of the same size, otherwise it would truncate them to the lower size.

Putting RAID considerations apart (because there are possibly countless possibilities), I believe you need to define three things:

  • What data are you going to store in the first set and how do you need to access it?
  • Are you really thinking your drives will fail eventually or you want a backup for safety reasons?
  • Does your hardware even support having 8 drives connected at one time?

The last one I think it is the most important. Not a user of recent hardware, but (normal) machines might have a tough time dealing with that amount of drives.

The first one is probably the cornerstone of your problem. If, for instance, I used your drives to store video files, to view later on, I don't think you would necessarily need to have all 6 drives joined in a RAID-0 setup; just store store until a drive becomes full.

Other than pure convenience (of not having to look 8 new letters, that you can configure, enable and disable, in Disk Management, to have just two at a time, for instance) I don't see a good reason to merge all those drives.

The second point is also relevant. Non RAID-0 setups (i.e. where data is actually written in more than one drive) are worthwhile if you expect a drive to fail. By fail I mean catastrophic fail, where you can't get your documents without resource to a specialist. For this to be worth it, you would need to secure your drives against anything, like fire, thefts, etcetera, as pointed in the comments.

If you want a simple backup for safety (of mind) you can use a software like Macrium Reflect (that has automatic differential backups, AFAIK, in the paid version) or, if you're feeling venturous, try to code it yourself, using tools like Python or try to search the Internet for a tool that suites your goals.

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  • Thanks for the replies... you are correct in that it is a hassle to get all the drives connected. my motherboard has 6 sata ports, and i need to extend with a pci express card for the remaining ports. I am setting up a media pc connected to a home cinema to store our digitalized dvd and blueray collection. I wanted to merge the drives for three reasons. 1: because these are large files of 4-30gb, if the drive is almost full, several GB may not be filled in the end, 2: it is a pain having to look trough 8 different volumes when looking for a file, 3: Easy backup between two large volumes.
    – Daniel
    Commented Sep 19, 2013 at 18:32
  • And, yes, I am assuming that there is only a matter of time before any drive will fail, which is why i am adding manual redundancy be mirroring two spanned volumes. This is about the best i can do, backing up terabytes of data to more than one location is expensive... it would take something like 200 single layer bluerays... though i am considering it as a more long-term backup medium. However, i do consider a 1 drive fail tolerance to be a good balance given the large amount of data and its medium importance...
    – Daniel
    Commented Sep 19, 2013 at 18:48
  • 1. From your usage, maximum amount of unused space would be 29.999 GB. You'll manage to fill your disks without worry. 2. I concede to that, but since you admitted to have just need for video files a simple database can be used, to avoid searching through folders (I assume you aren't going to move them) 3. I also concede but if you join the drives in RAID you may lose 500GB due to truncating. Then again, all this is valuable information you can add to your question. Maybe someone somewhere has a better solution than me and didn't see this question due to general terms.
    – Doktoro Reichard
    Commented Sep 19, 2013 at 18:49
  • Considering that there is 2 spanned volumes across 8 drives, this setup does allow more than one drive to fail at once, as long as they belong to the same volume...
    – Daniel
    Commented Sep 19, 2013 at 18:50
  • PS: yes, i have actually made a nice little console app in vb.net to do the backup file by file... it does differential copy, and replaces existing files if their crc32 checksum differs... :) i have set i to run once a day in task scheduler :)
    – Daniel
    Commented Sep 19, 2013 at 18:54

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