RAID1 questions

Discussion in 'Mac Accessories' started by Be3G, Feb 27, 2018.

  1. Be3G macrumors member

    Sep 19, 2007
    Hi all,

    I'm seeking a bit of advice before I set up some RAID1 storage. Though before I go any further let me just say now that I know RAID1 isn't a backup method, which is pretty much why I've never used it before. I have a good system of revolving/offsite backups involving multiple Time Capsules and external hard drives, but I'm soon going to be setting up a media centre Mac and I realised that my normal backup routines will be overkill for this Mac, because it will contain no personal data – just some TV recordings and iTunes purchases, the latter of which can mostly be redownloaded if needed.

    So I don't particularly need any protection against user error (I'll survive if I accidentally delete a recording of Doctor Who…) but I'd just like to mitigate against technical malfunction (mainly hard drive failure) as seamlessly as possible. I reckon that RAID1 fits the bill just right for this, because it's not something I'll have to manage – unless a drive fails and I have to swap/rebuild of course, but in that case it's done its job.

    With that in mind I'm considering a few different methods for configuring some RAID1 storage, and I'd appreciate the community's thoughts on how best to do this. I don't need high speed or huge amounts of capacity – just, say, 1TB of usable safe storage. To that end, I have a few questions:

    1. Which would be better – one external dual-HDD hardware RAID enclosure, one external dual-HDD JBOD enclosure using macOS software RAID, or two external single-HDD enclosures combined using macOS RAID?

    (My thinking is that the last option would be best, because with the first two a failure in the SATA bridge of the enclosure could result in corruption on both drives, whereas with the third option it's unlikely that the SATA bridge for both enclosures would fail simultaneously, so I should be able to rebuild the RAID.)

    2. Which external connection method (TB, FW800, USB3) would be best for reliability – by which I mean least likely to result in corrupt data, spurious ejections, or anything else you can think of?

    (My hunch is that TB/FW might be better as I generally have a low opinion of USB reliability, but I can't really quantify that so maybe I'm just being silly.)

    3. Which enclosure/drive type would be most reliable: 3.5" with external PSU, or 2.5" bus-powered?

    (I'm torn with this; conventional wisdom would seem to suggest that 3.5" is the way to go, but if I go for 2.5" then the lack of a separate power supply means there's one fewer point of failure in the setup.)

    Any input most gratefully received! :)
  2. jeyf macrumors 65816

    Jan 20, 2009
    raid 01 is "Disk mirroring" and basically cuts in half the MTBF of a given hard drive.
  3. Be3G thread starter macrumors member

    Sep 19, 2007
    (Note I'm talking/asking about RAID1, not 01 – that's something else entirely…)

    Well yes, using RAID1 mirroring does increase the chance of drive failure because there're two drives to fail rather than just one, but it means that in the event that one drive fails I can replace it with another without affecting the data, which is why I believe it'll be useful.
  4. jeyf macrumors 65816

    Jan 20, 2009
    what ever solution you need keep in mind mechanical storage is at its all time low cost
  5. Be3G thread starter macrumors member

    Sep 19, 2007
    After lots of research and also some experimenting, I've settled on a solution: software RAID1 using two USB single-drive enclosures with each containing a WD Red 2.5" disk. I figure that the 2.5" drives will be better suited to the cramped not-particularly-cool conditions of the cabinet that everything will be residing in compared to the normal 3.5" version. Still can't decide though whether to bus-power them or not, but considering the lack of mains-powered 2.5" enclosures on the market (OWC's On-The-Go Pro is the only one I can easily find) I probably will just let the USB connection supply the juice.

    In terms of deciding between USB and FW, I played around with an external drive earlier, copying files to it and doing various naughty things during that copy: force-unmounting, physically unplugging, and even switching the Mac off at the power. Using both connections it was surprisingly impossible to corrupt the drive, although the physical interruption methods did obviously result in the file being copied across at that moment showing as incomplete. So, pretty impressed by that.
  6. jeyf macrumors 65816

    Jan 20, 2009
    what you are doing is too much effort.
    Consider a 5 bay NAS box with full raid 05 protection.

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5 February 27, 2018