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Re: [zfs-discuss] question about COW and snapshots

Subject: Re: [zfs-discuss] question about COW and snapshots
From: Richard Elling
Date: Tue, 14 Jun 2011 20:56:51 -0700
On Jun 14, 2011, at 10:25 AM, Simon Walter wrote:

> I'm looking to create a NAS with versioning for non-technical users (Windows 
> and Mac). I want the users to be able to simply save a file, and a 
> revision/snapshot is created. I could use a revision control software like 
> SVN (it has autoversioning with WebDAV), and I will if this filesystem level 
> idea does not pan out. However, since this is a NAS for any files(Word, 
> JPEGs, MP3, etc), not just source code, I thought doing this at the 
> filesystem level via some kind of COW would be better.

I can't answer the "better" question, but with ZFS you can delegate to the user 
the ability to make
snapshots when they want. You can even have applications like databases make 
snapshots when
they want. Using this feature, you don't need to archive every write.

> So now my (ignorant) question: can ZFS make a snapshot every time it's 
> written to?

I hope not, that would suck most heinously.

> Can all writes be available as snapshots so all previous "versions" are 
> available?

That would suck worse.

> Or does one need to explicitly create a snapshot?


> I've read about auto-snapshot. But that seems like nice cron job (scheduled 
> snapshots). Am I mistaken?

No, that is how it works.

> I looked in to ext3cow, next3, and then some. ZFS seems the most stable and 
> ready for use. However, is the above possible? Or how is it possible? Is 
> there a better way of doing this? Other filesystems?
> Thanks for ideas and suggestions,

I use TimeMachine with a ZFS repository. It is time-based snapshots, too.
 -- richard

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