SnapRaid Parity on external drives connected via USB2: Dumb idea?

  • Hi All,

    I have a Silverstone DS380 8 bay case running 8 x 4TB drives using an old Intel i5 2500k based system and a firmware modded IBM M1015 disk controller. 7 of these drives are merged using UnionFS configured as data and content drives for SnapRaid with the 8th drive allocated as content and parity. Ideally I want more than one parity drive, however I also really need more storage space and I don't have the cash to replace the drives with something bigger. Everything is backed up to the cloud and currently I am deleting large files I don't have immediate need of to reclaim space (knowing I can restore from the cloud if need be).

    I do have a couple of spare 4TB drives though and I was thinking I might get a basic 2 bay external hard drive enclosure in which I could put these drives into. I have no free expansion slots on the motherboard of my OMV box, so I'd have to attach this external enclosure via USB2. To maximise the data access performance I was thinking I'd add these two disks in the external enclosure as parity disks. Once fully synced I'd then reconfigure the internal parity disk to be part of the UnionFS and add it into SnapRaid as a data/content disk.

    Does this sound like an ok plan given my situation? Are there any pitfalls of using external enclosures for parity disks?


    I see USB is specifically called out as not recommended;

    Not sure what option I have at present though. I'm the only user of this NAS, so provided the only impact of using USB is performance I think I'll just have to wear it. Ended up buying one of these as the seller had a refurb unit going cheap;…h-Enclosure/dp/B00LO3LUF6

  • I don't have any direct experience with USB and SnapRAID, but I don't think it should be too bad as a temporary solution. The issue is USB 2 itself: really too slow.

    Since parity is done only once a day (or whenever you set it up) it should not be an issue with USB3. Maybe consider adding a USB3 PCI-E card to your motherboard if there are no ports.

    But eventually this is not a nice solution.

    OMV BUILD - MY NAS KILLER - OMV 5.x + omvextrasorg

    Core i3-8300 - ASRock H370M-ITX/ac - 8GB RAM - Sandisk Ultra Flair 32GB (OMV), 256GB NVME SSD (Docker), 3x4TB HDD (Data) - Fractal Design Node 304 - Be quiet! Pure Power 11 350W

  • I only want to say, that use of USB drives are bad idea in general for a NAS, votdev have disable the RAID on it due a lot of problems in the past.

    allways try to use SATA and if you use USB, do not fear if something fails.

    PD: Usb as backup , and to copy only certain data from time to time is not bad idea, but use in a NAS all the time is.

  • Thanks for the feedback. Turns out I need to measure twice and cut once. I looked at the I/O panel of my OMV box prior to going down the USB route, turns out I completely missed an e-SATA port. Double whammy after actually getting the motherboard model number and reading the manual to find out it also has 2 x USB3.1 ports. For some reason I thought USB3+ only came out around 2015, tuns out I was way off the mark.

  • USB consortium just gone nut with the USB 3 naming.

    USB 3.1 Gen 1 is just a fancy way of saying USB 3.0.

    The same applies for USB 3.2 Gen 1, still old but good USB 3.0 at 5GB/s.

    This table should help.

    The Parity Drive will be better with USB3, but not ideal as I said earlier.

    OMV BUILD - MY NAS KILLER - OMV 5.x + omvextrasorg

    Core i3-8300 - ASRock H370M-ITX/ac - 8GB RAM - Sandisk Ultra Flair 32GB (OMV), 256GB NVME SSD (Docker), 3x4TB HDD (Data) - Fractal Design Node 304 - Be quiet! Pure Power 11 350W

  • While it's certainly not the best solution, I think you could do it.

    But, remember, your parity drives provides your ability to restore and, as others have already pointed out, USB is not known for solid reliability. In the scenario where you'd need to use USB connected parity disks to restore, the restoration of a 4TB drive would take a long time (a very long time over USB 2).

    Some thoughts:
    It seems you're outgrowing your storage.
    The first possibility might be to start swapping in 8TB drives, in place of the 4TB drives.

    If it was me, I'd start building a new server with much larger drives. As much as you have stored, if you're stretching the capacity of 4TB X 8 Drives, you need to be thinking about a backup server for some redundancy in any case. Cloud storage is useful for backing up important files but restoration of bulk data is not fast.

  • My setup is as below - I have used USB 3 Seagate 2.5" 5TB drive as parity for around six weeks, no problems so far - it is accessed once a day using a snapraid helper script. No expereince of restoring as yet.

    Inwin MS04 case with 315 W PSU

    ASUS Prime H310i-Plus R2.0 board

    Four port PCI-E SATA card

    8GB Kingston DDR4

    Intel Pentium Coffee Lake G5400 CPU

    Samsung Evo M.2 256GB OS drive (28 GB partitioned for OS)

    4x4TB WD Red NAS drives - UnionFS pool

    Seagate 5TB USB drive - SnapRAID parity

    1x1TB Seagate HD

    1x300GB Toshiba HD

    Seagate 2TB USB drive

    Edited once, last by johnvick ().

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