Date: Fri, 1 Mar 2013 06:28:57 -0900 From: Royce Williams <royce@tycho.org> To: Ronald Klop <ronald-freebsd8@klop.yi.org> Cc: freebsd-stable <freebsd-stable@freebsd.org>, Karl Denninger <karl@denninger.net> Subject: Re: Musings on ZFS Backup strategies Message-ID: <CA%2BE3k93kQYGxmuhapqAExZXZwP0qgCLBv537J1pB0bnTz=T%2BZw@mail.gmail.com> In-Reply-To: <op.ws9v8fvs8527sy@ronaldradial.versatec.local> References: <5130BA35.5060809@denninger.net> <op.ws9v8fvs8527sy@ronaldradial.versatec.local>
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On Fri, Mar 1, 2013 at 6:06 AM, Ronald Klop <ronald-freebsd8@klop.yi.org> wrote: > On Fri, 01 Mar 2013 15:24:53 +0100, Karl Denninger <karl@denninger.net> > wrote: > >> Dabbling with ZFS now, and giving some thought to how to handle backup >> strategies. >> >> ZFS' snapshot capabilities have forced me to re-think the way that I've >> handled this. Previously near-line (and offline) backup was focused on >> being able to handle both disasters (e.g. RAID adapter goes nuts and >> scribbles on the entire contents of the array), a double-disk (or worse) >> failure, or the obvious (e.g. fire, etc) along with the "aw crap, I just >> rm -rf'd something I'd rather not!" >> >> ZFS makes snapshots very cheap, which means you can resolve the "aw >> crap" situation without resorting to backups at all. This turns the >> backup situation into a disaster recovery one. >> >> And that in turn seems to say that the ideal strategy looks more like: >> >> Take a base snapshot immediately and zfs send it to offline storage. >> Take an incremental at some interval (appropriate for disaster recovery) >> and zfs send THAT to stable storage. >> >> If I then restore the base and snapshot, I get back to where I was when >> the latest snapshot was taken. I don't need to keep the incremental >> snapshot for longer than it takes to zfs send it, so I can do: >> >> zfs snapshot pool/some-filesystem@unique-label >> zfs send -i pool/some-filesystem@base pool/some-filesystem@unique-label >> zfs destroy pool/some-filesystem@unique-label >> >> and that seems to work (and restore) just fine. >> >> Am I looking at this the right way here? Provided that the base backup >> and incremental are both readable, it appears that I have the disaster >> case covered, and the online snapshot increments and retention are >> easily adjusted and cover the "oops" situations without having to resort >> to the backups at all. >> >> This in turn means that keeping more than two incremental dumps offline >> has little or no value; the second merely being taken to insure that >> there is always at least one that has been written to completion without >> error to apply on top of the base. That in turn makes the backup >> storage requirement based only on entropy in the filesystem and not time >> (where the "tower of Hanoi" style dump hierarchy imposed both a time AND >> entropy cost on backup media.) >> >> Am I missing something here? >> >> (Yes, I know, I've been a ZFS resister.... ;-)) >> > > I do the same. I only use zfs send -I (capital i) so I have all the > snapshots on the backup also. > That way the data survives an oops (rm -r) and a fire at the same time. :-) Concur. There are "disasters" that are not obvious until some time has passed -- such as security breaches, application problems that cause quiet data corruption, etc. I do not know how a live ZFS filesystem could be manipulated by an intruder, but the possibility is there. -- Royce Williams
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