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Re: [zfs-discuss] questions on zfs send,receive,backups

Subject: Re: [zfs-discuss] questions on zfs send,receive,backups
From: Richard Elling
Date: Mon, 03 Nov 2008 08:22:19 -0800
Ross Smith wrote:
>> Snapshots are not replacements for traditional backup/restore features.
>> If you need the latter, use what is currently available on the market.
>> -- richard
> I'd actually say snapshots do a better job in some circumstances.
> Certainly they're being used that way by the desktop team:
> http://blogs.sun.com/erwann/entry/zfs_on_the_desktop_zfs

Yes, this is one of the intended uses of snapshots.  But snapshots do
not replace backup/restore systems.

> None of this is stuff I'm after personally btw.  This was just my
> attempt to interpret the request of the OP.
> Although having said that, the ability to restore single files as fast
> as you can restore a whole snapshot would be a nice feature.  Is that
> something that would be possible?
> Say you had a ZFS filesystem containing a 20GB file, with a recent
> snapshot.  Is it technically feasible to restore that file by itself
> in the same way a whole filesystem is rolled back with "zfs restore"?


> If the file still existed, would this be a case of redirecting the
> file's top level block (dnode?) to the one from the snapshot?  If the
> file had been deleted, could you just copy that one block?
> Is it that simple, or is there a level of interaction between files
> and snapshots that I've missed (I've glanced through the tech specs,
> but I'm a long way from fully understanding them).

It is as simple as a cp, or drag-n-drop in Nautilus.  The snapshot is 
read-only, so
there is no need to cp, as long as you don't want to modify it or 
destroy the snapshot.
 -- richard

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