Raid Dilemma / Confusion

[ptmuldoon]

I understand Proxmox (and most hypervisors) do not support software raid, and I can understand the reasons for that. But I'm unsure of how I should proceed and maybe I'm just confusing myself. BTW, ....everything I am doing is simply for a home server/project and learning experience.

I currently have a 4x1TB raid 5 setup in UbuntuServer. The current OS is on a compact flash with the 4 drive raid setup purely holding Media.

Now if I create a guest OS of UbuntuServer in ProxMox, there is no 'simple' way to move the raid onto the Guest OS. I read it is possible to attach a physical drive to a ProxMox Guest, but I believe that's considered bad practice in a Hypervisor setup?

So is the below the best approach to take?

My plan was to install ProxMox onto a 500GB drive, with that drive hosting just ProxMox, and probably the various Guest OS's. Then to use a hardware controller raid setup of multiple drives for the various media/data storage. I would than look to convert each existing physical disk in my current raid setup to a virtual disk. Than you would recreate the raid in the guest OS using the virtual disks?

My one question is are you losing disk space by first having a hardware raid say of 5x1TB drives in raid 5 setup. That provides about 4TB of actual usable space. And than when you create your virtual disks, and create 4X1TB virtual drives in a raid 5. Area you really giving yourself only 3TB of space? So you actually lose 2TB of space? Or do I misunderstand how a virtual raid array would work?

Thanks for any help, and teaching a newbie

 

[marotori]

I am rather confused by what you are trying to do.

If you have the host machine configured to use hardware raid 5, then there is absolutely no point creating a guest machine with 5 drives and software raid inside it. You are essentially double raiding and introducing a layer of software io for no reason.

Just make one virtual drive (as an image) and store it on the raid array.

 

[ptmuldoon]

That's exactly what I thought, but.......... Is there a maximum size of a Virtual Disk than? My current Raid 5 setup has about 3.5TB in media, and anticipates to grow. I'm unsure where I read it, and if it related to proxmox or another hypervisor that a Virtual Disk shouldn't exceed 2TB?

 

[WaltervdSchee]

I'm using a Hardware RAID controller (HighPoint RR 3520 (Intel IOP-based)) to expose a 8TB (4x 2TB RAID-0) device on the host,
to a virtual SCSI disk on my fileserver VM, (Linux).
No problems here...

 

[Milkwyrm]

The 2TB limitation applies to ESX server for local storage. I'm afraid I cant remember of the top of my head if that also applies to LUN size on external storage.
It is one of the more annoying limitations when building a stand alone ESX server. (I cant comment on Hyper-V or Citrix, not having worked with those two products)

 

[ptmuldoon]

Thanks guys. So I should have no limits/concerns then on a very large virtual disk. I believe from a performance standpoint, HW gives better (but maybe not much) performance that SW raid? But I've still always been concerned about hardware raid vs. software raid.

Am I correct that with HW raid and if your controller goes, you are SOL unless you have an identical card as a spare? The nice thing about software raid is its ease to move between PC's and not being hardware dependent.

Isn't the same true if using your mother board's raid? I Think its generally referred to as BIOS raid? But wouldn't the same apply as hardware raid? If your MB dies, are you screwed?

And finally....... What would be the easiest way to move a 4 disk software raid 5 array to a Virtual disk? easiest would likely be get new drives setup in a hardware raid, create the Virtual disk, and move the data with rsync or similar?