Question about Snapid - how many drives at minimum? Does it make sense compared to single drives?

FFrank · 7. Januar 2019

Hi,
since some weeks I am setting up my OMV and I start to love it.

First I had it setup as Raid 1 - see here:
Changing Raid1 to 2 single disks

Now I have it with 2 single drives and I am thinking how to proceed.

a) Setup RSync or similar to protect my data
b) Setup a Snapraid to protect my data

I am planning to do a USB Backup on a large external USB drive from time to time as a backup. I know, RAID is not a backup

My use case:
I want to use it as a file server for my pictures (a little more than 1 TB) for my music (played via Volumio on a RasPi) and as a place to write backups from some Windows PCs.

What I like about Snapraid is the fact that I can just put in some more discs if space is getting tight and all shares are stay the same. This is not this simple in a single disc solution - I would reorganize all my shares and backup routines...right?

I am reading for some hours now and I learned that I have to have the largest disk as a parity disc. But what is the minimal HDD number I need for a setup with Snapraid to protect a single failure?

To make it short, here are my questions:

- for my use case, is it worth the effort?
- is it a good idea to use ext4 as filesystem?
- can I start with just 2 HDDs or do I need 3?
- ^{What is the difference between data and content drives?}

^{- Where do I find a list about usable space if I use 3 * 3TB discs for example?}

^{Thanks for your advice/thoughts about it - or some links to get more information I am missing...and sorry for my English - not a native speaker...}

^Best.

^Fabian

KM0201 · 7. Januar 2019

Well, considering Snapraid requires a parity drive, I would think the minimum is 3 drives... but I don't use it so I'm not sure.

That said.. 2 drives.. I'd use rsync and forget about it. Get a 3rd drive, pop it in an enclosure and have an external backup as well that you can either keep in the safe, or keep it off site.. Scheduling them is a little complicated (and frankly, a little odd, IMO).. but once you get the hang of it, it's easy... Or, just leave it off and log in and do it yourself a couple times a day and do it manually

I leave the delete trigger off, then once a month or so when I'm sure I've not accidentally deleted something, I log in and enable the delete trigger then manually run the job. That brings the two drives completely in sync, and also gives a modicum of security against accidental file deletion, etc. If I do accidentally delete something.. I just ssh my NAS and cd to the "mirror" drive, find the file i accidentally deleted and move it back to the "source" drive.

It's extremely simple and far superior to Raid 1, not really sure on Snapraid as I've never used it.

macom · 7. Januar 2019

Alternative to rsync would be rsnapshot. There is a plugin for it.
Advantage: as the name indicates it will create snapshots. So you have the possibility to go back in time and restore previous versions of a file.

FFrank · 10. Januar 2019

Any more answers concerning snapraid?
Would like something about this:
- Where do I find a list about usable space if I use 3 * 3TB discs for example?
- is it a good idea to use ext4 as filesystem together with unionfs?

And one new:
- Will Snapraid speed up things like a raid?

Thanks.
Fabian

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