2 Replies Latest reply: Nov 19, 2012 9:27 PM by Mike Stitzer
Mike Stitzer Level 1 (55 points)

Hi all,


I wasn't sure if this is the best place to ask it, as I'm not running OS X Server, but I am running a Mac as a home server so it seems like the best fit...


I have an always-on Mac acting as the iTunes server for various Apple TVs, as well as the central iPhoto station (syncing and editing) from all of the family's iOS devices. Right now I've got several external USB2 and USB3 disks totalling 8TB acting for additional storage, with 6TB used, and most of that is NOT backed up. The Time Capsule only has enough space for the imporant documents from all our Macs (photos, documents, apps, etc.).


I was originally debating buying a Synology or Drobo product, or building my own NAS, but since the Mac is always-on and they all cost so much I've started to drift away from that. At this point, I'm thinking my needs will be best served simply by 4 large external USB3 HDDs, 2 for files and 2 for backup, as I can get a 4TB for about $220.


So the big question becomes: is it a safe/good idea to use Disk Utility to create 2 concatenated sets of 8TB via USB3? I've never done this, and while I'd be maintaining one set as a nightly backup for the other via CCC or SuperDuper, if there are horror stories out there of this set-up I might as well not bother. It would only be for convenience of having the iTunes library on one concatenated disk set with iTunes auto-managing it. Right now it's too big to fit on a single 4TB drive.


So has anyone done concatenated sets over USB3?

  • John Lockwood Level 5 (7,220 points)

    I believe that converting your existing external drives to a concatenated set will require erasing them. As they are no backed up this sounds like it would not be what you want to do.


    Also I would regard a concatened set as being at greater risk than several individual disks as a single failure would affect them all since the volume would be spread across multiple disks.


    Your original idea of having a proper RAID protected NAS box is the best one. You can then configured iTunes running on your Mac to store everything on the NAS.

  • Mike Stitzer Level 1 (55 points)

    Hi John,


    I'm aware that creating a concatenated set will erase the files. I would only do so after buying the extra 4TB disks and creating backup of all my files. I am also aware of the increased risk of drive failure, but this would not be a very high risk [(MTBF disk 1 + MTBF disk 2)/2] when dealing with a backed up set.


    Still, at this point I'm thinking of maybe doing a concatenated 7TB set of two disks backed up to two separate 4TB disks via SuperDuper or CCC. That way the backups don't have the same risk of increased failure. Or maybe I'll just stick with 4 separate disks with the iTunes Library split and manually managed, as that will be the simplest, cheapest, and least complicated of all solutions.


    The problem with a NAS using RAID is as follows: RAID = redundancy, but RAID ≠ backup, so I have no protection from enclosure failure, disk failure leading to enclosure failure (I've found recent horror stories on the net, mostly for Drobos), or software corrupting the data. The other problem is an empty NAS from Synology or Drobo costs the same as 3 external 4TB USB3 drives. And then I'd still have to buy the drives!


    So I could have 24TB (12 for data and 12 for backup) in external HDDs or 12TB in a fancy case without backup but with redundancy. Or I could spend half the money, which is what I intend to do at this point. The question now is whether the concatenated set is worth it.


    At this point, unless someone posts here with a horror story or links to horror stories when using USB3 for concatenated sets, I'll give it a try and update this in a several weeks.