RAID with Raspberry Pi

    • OMV 3.x
    • Hi,

      I have a problem with last build OMV_3_0_99_RaspberryPi_2_3_4.9.80.img
      I have a Raspberry 3 B+ and Raspberry 3 B with the same problem for both of them

      I did a fresh install into a USB Card and installed it.
      After, I have 3.0.79 version of OMV and kernel 4.9.80-v7. In the RAID menu, I found my two disks (/dev/sda and /dev/sdb).

      Then I waited for the update and reboot.
      After, I have 3.0.99 version of OMV and kernel 4.14.30-v7. And in the RAID menu, I don't find my two disks. It's empty !
      I can't create a RAID 1 with my two disks.

      Do you have a solution to resolve my problem?

      Thanks

    • hadramos wrote:

      Do you have a solution to resolve my problem?
      I recommend not using raid with usb and highly recommend not using raid on a RPi.
      omv 4.1.13 arrakis | 64 bit | 4.15 proxmox kernel | omvextrasorg 4.1.13
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      Please read this before posting a question and this and this for docker questions.
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    • RAID over USB has known problems, such as the one you're experiencing. The USB interface (there's several flavors) may "filter" some the characteristics of the drive, fail to pass drive ATA commands, delay the assembly of the array, etc. While USB may work in some cases, it's not as reliable as using a hard drive interface. If RAID is a hard requirement, drives should be connected with sata or sas ports.

      Adding to the USB issues, for software RAID, an R-PI is too slow.
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    • RAID with Raspberry Pi

      The first question you should ask yourself is why you want to play RAID. Most probably the answer has something to do with data protection and then you're already wrong (RAID is not backup).

      RAID-1 only protects from a hard drive fail (happens not that often) and doesn't provide any more benefits. It's all about increased availability and reliability.

      If you are concerned about availability and reliability why do you choose then the most crappy platform possible? Every Raspberry Pis from a NAS point of view is just horribly unreliable and way too slow anyway.
      • Those things suffer from underpowering problems
      • The CPU has only one single USB2 connection to the outside
      • If you want to access USB storage you want to use UAS (USB Attached SCSI). Cheap SBC like an Orange Pi Zero for $7 can do UAS but Raspberries not (they're only capable of the old and slow BOT mode)
      • Every disks connected to a Pi is behind the same internal USB hub
      • Even the Ethernet interface is behind the internal USB hub
      • On RPi 3 B+ it's not just one internal USB hub but two cascaded ones (they managed to make things even worse)
      • All devices behind these internal USB hubs have not only to share bandwidth but add to USB bus contention problems
      • The internal USB hub is a so called SPoF (single point of failure -- RAID is all and only about eliminating those!!!)
      Adding to this: to access USB disks flawlessly you need a perfectly working USB-to-SATA bridge inside the drive enclosure (99% of USB disks connected to a Pi do not apply). RAID rebuild times are horrible since bottlenecked by the single USB2 connection and shared bus. The time a rebuild takes your array has no redundancy any more. Such a RAID rebuild is disk and bus stress. What if now the most prominent SPoF on these thingies fails? When the internal USB hub decides to fail with heavy RAID accesses your whole array is gone instantly.

      RAID with USB disks is already insane given the many problems that prevent reliable operation. USB RAID with all disks behind one USB2 hub is close to stupid. Do yourself a favour and don't try this. It's a useless waste of at least one disk and the setup will fail when needed anyway (RAID rebuild after a disk failure, maybe even before. Just search the forum or see here directly).
    • tkaiser wrote:

      The first question you should ask yourself is why you want to play RAID. Most probably the answer has something to do with data protection and then you're already wrong (RAID is not backup).

      RAID-1 only protects from a hard drive fail (happens not that often) and doesn't provide any more benefits. It's all about increased availability and reliability.

      If you are concerned about availability and reliability why do you choose then the most crappy platform possible? Every Raspberry Pis from a NAS point of view is just horribly unreliable and way too slow anyway.
      • Those things suffer from underpowering problems
      • The CPU has only one single USB2 connection to the outside
      • If you want to access USB storage you want to use UAS (USB Attached SCSI). Cheap SBC like an Orange Pi Zero for $7 can do UAS but Raspberries not (they're only capable of the old and slow BOT mode)
      • Every disks connected to a Pi is behind the same internal USB hub
      • Even the Ethernet interface is behind the internal USB hub
      • On RPi 3 B+ it's not just one internal USB hub but two cascaded ones (they managed to make things even worse)
      • All devices behind these internal USB hubs have not only to share bandwidth but add to USB bus contention problems
      • The internal USB hub is a so called SPoF (single point of failure -- RAID is all and only about eliminating those!!!)
      Adding to this: to access USB disks flawlessly you need a perfectly working USB-to-SATA bridge inside the drive enclosure (99% of USB disks connected to a Pi do not apply). RAID rebuild times are horrible since bottlenecked by the single USB2 connection and shared bus. The time a rebuild takes your array has no redundancy any more. Such a RAID rebuild is disk and bus stress. What if now the most prominent SPoF on these thingies fails? When the internal USB hub decides to fail with heavy RAID accesses your whole array is gone instantly.

      RAID with USB disks is already insane given the many problems that prevent reliable operation. USB RAID with all disks behind one USB2 hub is close to stupid. Do yourself a favour and don't try this. It's a useless waste of at least one disk and the setup will fail when needed anyway (RAID rebuild after a disk failure, maybe even before. Just search the forum or see here directly).
      Thanks you very much for your explain. You have open my eyes for RAID via RPi. For me, RPI is not expensive. And the RAID it's just perfect for me for data protection (in addition to a backup).

      OMV it's just perfect for a home NAS. I use this :)
    • hadramos wrote:

      And the RAID it's just perfect for me for data protection
      Again: RAID does NOT provide any means of data protection. It's only about increased availability (one disk fails but operation can continue without manual intervention -- that's the idea, often it doesn't work that way since hardware is too crappy, users do not test appropriately and are then surprised that their whole array has gone with the first failing disk).

      Availability (business continuity) is all what RAID is about (leaving aside the performance aspects when running larger RAID arrays on server grade hardware and not on toys).

      If you do RAID for data protection then you do it wrong. If you want to play RAID on a Raspberry toy you're doing wrong too. The hardware is way too unreliable to be able to increase reliability or to provide higher availability.

      If you're fine with abysmal NAS performance and some reliability issues then a Raspberry Pi is fine as single disk NAS. But that's it. And for the low performance these things are way too expensive.