Dear Daniel,
Thank you for your reply. Yes - you've described exactly what it is that I'm trying to do. And you're right - I am probably over-thinking it! Just want to be sure that what I think it happening actually is, if you see what I mean. Anyway, thank you for your explanation. Between that and Colin's recent mails, I think I understand things well enough now to go ahead. Regards, John ## On 21-03-2014 19:26, Daniel Staal wrote: > --As of March 21, 2014 3:13:58 PM +0000, John Gamble is alleged to have > said: > >> Thanks again for your reply. Still slightly confused about this process >> though…. In the scenario I'm thinking about, 'backup-wednesday.part' and >> 'backup-thursday' wouldn't have any common files (or blocks of data). The >> complete archive would be the sum of 'backup-wednesday.part' and >> 'backup-thursday'. Therefore, how is it possible to delete >> 'backup-wednesday.part'? Is it, in fact, impossible to do so in this case? >> If so, is there any way to create a single complete backup/archive from two >> or more partial ones, that were formed by premature termination of a backup. > > If there are truly no files in common, then deleting backup-wednsday.part > deletes all the files (or: data blocks containing files) in that backup. > But if that's the case, then the complete archive is *not* the sum of the > two: You have two separate archives. > > What I think you want to do is back up a list of files, break up the > connection, then finish the backup of that list of files at another time. > Tarsnap can do this easily, as long as you don't overthink it. ;) In > particular, do *not* try to exclude the files that you have 'successfully' > backed up on Wednesday from the Thursday backup. Just let it back up > everything again; tarsnap will figure out what it has already sent and what > it hasn't, and handle things appropriately. > > Tarsnap is designed to handle nicely the common backup situation where you > are backing up a large number of files on a regular basis, without caring > or knowing when they are changed. (Or created, or deleted.) You give it a > list of files and it backs up *what it hasn't backed up before* of that > list. Partials are just backups that didn't run to completion: They don't > have all the files they are supposed to, but other than that they are > normal archives. (There is no difference to *tarsnap* between a partial > and a full backup - it just names them as partials so that the *user* can > tell the difference.) > > Another way to look at this (slightly inaccurate, but will probably help > understanding): The list of files in a backup is created at the start of > the backup process. Tarsnap turns that into a list of data blocks that it > has to save to the server. It then checks to see if it already has any of > those blocks on the server, and skips those, while sending the rest. A > partial backup is one where that didn't complete - but the blocks that it > has sent are still there. If you then create a new backup with the same > list of files, there will be more blocks tarsnap can skip sending. (But > note that the *list of files* is identical - tarsnap just didn't complete > sending them the first time.) > >> I'm asking all this because given the speed of my upload connection, I know >> that I'll have to stop the initial backup before it completes. Just wanted >> to make sure that I'll ultimately be able to create a complete backup. > > Yes, just keep creating the backup with the same list of files and let > tarsnap handle sending what data it needs to. (My initial upload of one of > my archives took over a month, and was broken up several times, but created > a complete archive in the end.) > >> A couple of minor queries: 1). To terminate an ongoing backup, is the >> command ^Q? > > That or ^C (SIGINT), or SIGQUIT will work, in my experience. ;) > >> 2). While the backup is ongoing, is it OK to use the computer as normal? > > Yes. Be aware that there will be a fair amount of IO going on, both disk > and network, but other than that you should have no problem. > > If you are working with the files that you are backup, be aware that > tarsnap does not by default do a 'point in time' backup - it will backup > the file in the state it is in when it gets to it, even if it's been edited > since the backup started. (If it gets deleted, you'll get an error > message, but tarsnap will continue on.) If you need a point in time > backup, you'll have to look at filesystem snapshots. Most of the time you > don't, unless you are trying to back up an active database or something > like that. > > Daniel T. Staal > > --------------------------------------------------------------- > This email copyright the author. Unless otherwise noted, you > are expressly allowed to retransmit, quote, or otherwise use > the contents for non-commercial purposes. This copyright will > expire 5 years after the author's death, or in 30 years, > whichever is longer, unless such a period is in excess of > local copyright law. > --------------------------------------------------------------- -- The Wellcome Trust Sanger Institute is operated by Genome Research Limited, a charity registered in England with number 1021457 and a company registered in England with number 2742969, whose registered office is 215 Euston Road, London, NW1 2BE.
