Raid Questions?

    • OMV 3.x
    • Raid Questions?

      Hi, I set up OMV in a VM, with the following drives,

      8GB, 12GB, 15GB, 10GB, 8GB, 10GB, 11GB, 15GB, 20GB, 8GB, 8GB

      This totals 110GB. But when I set up raid 5, I got 71.93GB, and with raid 6 I got 63.94GB.

      I can conclude from that it doesn't play nicely with drives of differing sizes, am I correct? Is it only using 8GB from each drive?

      I thought a file system such as EXT4 was for a single drive? How can I build a raid array and then format it EXT4? What technology is the raid array being built with?

      If I can use EXT4 across drives then what advantage would XFS give?

      The post was edited 1 time, last by petermc ().

    • Any RAID array will use the lowest drive size across the array.

      With a RAID array you would want x amount of not only the same size drive, but the same model as well for all drives in the array.
      OMV 4.x
      Supermicro X9DRH-7F
      2X-XEON E5-2660V2
      32GB PC3-10600R ECC REG
      Supermicro SATA DOM 64GB
      Areca ARC-1883IX-24
      24X - WD WD80EFZX
      NORCO RPC-4224 4U
      Eaton 5PX 1500
    • mikebetz42 wrote:

      Any RAID array will use the lowest drive size across the array.
      Nope, not any RAID does so. But at least with mdraid's RAIDD5 and RAID6 modes it works that way.

      petermc wrote:

      I thought a file system such as EXT4 was for a single drive?
      A traditional filesystem is applied to a block device which can be a single drive or an mdraid. There exist way more better approaches in the meantime but the obvious first question you should ask (yourself): why do you want to implement RAID? If 'data protection' is part of the answer you're already doing it wrong. If you're only looking for data availability then you're doing it somewhat right :)
    • Nibb31 wrote:

      Drives that size must be super old and power-inefficient.
      He's playing RAID in a virtual machine. Those virtual block devices are most probably simple files or disk containers in reality.

      Anyway: since it's about playing RAID in a VM two things are diffent compared to RAID with physical disks
      • When playing RAID with physical drives in pass-through mode by the Virtualization software a single drive fail might stop the whole VM. If RAID is implemented to get higher availability in case a drive fails this won't happen. You waste one or more drives simply for nothing (this does not apply to the situation of this thread, I'm talking about a general problem for many people running OMV productive in a VM)
      • When trying to simulate disk failures in an experimental VM with disk containers (as it's done here) you should be prepared that 'physical drive failure' looks entirely different compared to you clicking a virtual disk away in your VM environment. Total drive fails can be somewhat emulated but not what happens way more often: drives starting to die slowly
      OMV in a VM is a nice way to try out certain things, RAID even amongst them. But please don't draw the wrong conclusions wrt availability and reliability. A VM environment behaves pretty different compared to a real world setup with physical disks.

      @petermc: There's nothing wrong with trying out things in a VM but I would strongly recommend reading through some basics first before trying RAID. What's the purpose of the thing, what are pros/cons and inevitable drawbacks. Any technology that adds complexity needs to be fully understood prior to productive usage :)