Why use greyhole vs Proxmox's LVM

olson
Posts: 30
Joined: Mon Dec 03, 2012 7:57 am

Why use greyhole vs Proxmox's LVM

Postby olson » Sun Jul 21, 2013 1:34 pm

Hello all,

I have not used proxmox yet. I am doing my initial research to see how to set it up.

On my existing HDA (dead, won't post) I used a small drive for amahi, then had 3 large drives as my storage, one was a parity drive for snapraid. I used greyhole to pool the 2 (non-parity) drives. I want to combine my HDA server w/ my mythtv backend server (which I built in 2002... and its only had a hard drive replacement :P and been running almost 24/7 since I built it) on proxmox.

So my question, why not use proxmox LVM as your "pool" within your amahi VM? I don't have a lot of LVM experience so that question might not make much sense.

In the amahi wiki, it looks like the writer is giving the amahi VM direct access to the drives to use grey hole for your pooling. Why not use NFS to give amahi access to a folder in the LVM?

Having never used LVM, I don't know if this is ok or not. LVM kinda scares me since loosing one drive kinda kills the whole "pool" (i think).

My plans are to use snapraid running on the proxmox install. This would limit my worries about loosing an LVM drive.

Is making all my drives part of the LVM a bad idea?

User avatar
sgtfoo
Posts: 419
Joined: Sun Jul 18, 2010 8:27 pm

Re: Why use greyhole vs Proxmox's LVM

Postby sgtfoo » Tue Jul 23, 2013 5:17 am

Using LVM vs greyhole is a matter of preference for how you're setup and how you want your data accessible.
LVM within Proxmox is there to facilitate expanding storage for proxmox images, ISOs, containers, etc. It can contain virtual drives that you can assign to your HDA VM.
Using greyhole can imply using any combination of physical drive mounts, virtual drive mounts or iSCSI mounts, or any such thing.
You should read up and understand that greyhole and LVM are not the "same type of thing".
Greyhole is a way to have folder-level duplication across multiple volumes (not necessarily drives)
LVM is a way to amalgamate multiple physical volumes into a logical set that can be partitioned like a physical one.
What and how you use them in tandem or not for your needs is up to you and your needs.
The prime difference in terms of merging volumes, which both technologies essentially do for you, is that Greyhole does folder-level duplication, but LVM does not.

For example:

1) Use 3 drive images that reside within your "local" LVM storage in Proxmox, and have greyhole use those 3. It's just that this type of setup becomes inherently slower because of the additional overhead. If all your physical drives are SUPER fast, then it's fine, but for consumer-grade drives (7200RPM) this can be slow. The benefit is that Greyhole can have duplication.

OR

2)Use 2 physical drives connected to your hardware Proxmox machine and have greyhole see them exclusively for usage (no LVM involved)

OR

3) nested LVM of drives that are images that reside in the "local" Proxmox LVM storage. Nested LVM seems troublesome and confusing.
SgtFoo
HDA: VM inside oVirt FX-8300 95w (2 cores for HDA), 32GB RAM (2GB for HDA)
My PC: FX-8300, 16GB RAM, 3x 1TB HDDs, Radeon HD6970 2GB video; Win10 Pro x64
Other: PC, Asus 1215n (LXLE), Debian openZFS server (3x(2x2tb) mirrors)
Modem&Network: Thomson DCM475; Asus RT-AC66U; HP 1800-24G switch

olson
Posts: 30
Joined: Mon Dec 03, 2012 7:57 am

Re: Why use greyhole vs Proxmox's LVM

Postby olson » Tue Jul 23, 2013 7:18 am

Thanks for the post... that helps me out.

I've done a bunch of research in the past couple of days and I dislike the sound of LVM. Sounds like a pain if you have a drive fail and it seems to complicate things.

I've done a lot of research for ZFS, aufs, software raid, etc.... in the end, I think I've decided to just keep using snapraid. Combine that with AUFS or keep using greyhole...

Now I have to decide on proxmox vs esxi... I'll probably go proxmox and run snapraid directly from it.

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