Databases, like MySQL, Oracle, or even Microsoft Exchange (the email server), must be 'quiesce' either by putting them in a 'quiescent state' or taking the database/software down so it is not running. This is because they are changing what is on disk whenever it has a need (email comes in, or a update to the database, addition or deletion). To be active while it is quiesced, the database systems start writing all changes (or adds, or deletion information) to a journal that is not 'posted' till after the back up completed. Then in a flurry of activity all the transactions are posted, in order, what seems like all at once. The logic is more convoluted than that, but it is an over simplification for example purposes.
How do I know that? I spent about 20 years of my 35 year IT career handling backups and interactive systems that relied on transaction oriented data bases. IMHO, there are three kinds of backups, (1) the 'Oh S**T' backup, to recover a file or a few for the person who just wiped out a document or presentation they need completed right now. Preferably the latest thing available (how about 5 minutes ago?) - very few systems do this. The operating system Plan 9 from Bell Labs (written as an exercise to make UNIX better, but never went man stream) is one of the few that took care of this as a part of its architecture. Some backup systems today for the home user try, like Crashplan (or Mozy, or Carbonite, or ... whoever) doing 5 minute incremental backup of home directories, etc. Most businesses don't deal with this. (2) the Business backup - daily backups of normal files and things that matter. Documents, presentations, spread sheets of data. - This is the daily backup most businesses do. They may or may not do 'database backups' or may do them separately but on the same 'clock' or calendar. (3) Disaster Recovery - this is the backups you get from off site that you do weekly, monthly, yearly? to get back up and running after you rebuild the data center or your house after the tornado or hurricane or tsunami or flood or fire. Working for banks and fortune 500 companies, this is a monster pain to prepare for. But we tested the recovery at least every 6 months, typically 3. The first 3 times we did that for a major oil company we failed, then we were able to recover almost everything within 12 hours (our test window was 48 hours for each attempt). We succeeded every time afterward. Working for banks, we had to test every 3 months and document it all for auditors (state, federal, business contingency and continuity, and internal, and external audits, all every year ... yep, a LOT of overhead). We failed at times, we succeeded mostly. (Story: I had a boss complaining about the cost of backups and testing. I told him I would be glad to stop, remove the servers, then quit, but first I wanted him to get an insurance company - like Lloyd's of London - to quote on a policy to cover the shareholders and bank stake holders for the risk of NOT doing what we do. ... He never got back to me on that.) All this is to say backups is a big deal. Please do it carefully and test your backups. You don't have to restore EVERYTHING. But do 'test restores' on a 'statistical method' (randomly choose a couple of files at different places on your system, and copy them somewhere you can get them back. Then use your software to restore the files. This will give you a pretty good feel for the ease and ability to get the information back. Doing it on systems (like database servers, or big application systems) where data consistency is required to keep things running, there are a few ways to get it done 'right'. (1) stop the system, make backups, restart the system. Or a modification I did quite a bit (2) quiesce the system, make a backup to other high speed disks, start the system, then backup the 'copy' we made to disks. At some time, you still have to test restoring and bringing the system up to ensure it works with the stored data. Another thing is 3-2-1 of Backups. (3) Have at least 3 copies of the data. (1.Live data, 2.backup 1, 3.backup 2). (2) Use at least 2 different media (1. Disk, 2. Tape, 3.DVD/CD, 4.Commercial offsite backup) (1) One copy must be kept off site. - If you use a commercial off site, that is OK. If you use other media, it needs to be off site. Another town is good. Across country is better. But at least take it from the office and put it in a fire proof case in your closet at home (in a building several blocks from the office!) (0) Test your backups to ensure you can restore data from any and all backup sets on a regular basis (quarterly? annually? you choose, but do it) Yes, I am a computer professional.. I have lost data. Some of it mine and my family. Some of my employers. I have eaten many portions of crow and humble pie over the years. It is always tough and hard to digest. Please do as I suggest, not as I have done. ... Jack in TN On Mon, Mar 7, 2016 at 12:55 PM, Guus Snijders <gsnijd...@gmail.com> wrote: > Op 7 mrt. 2016 14:02 schreef "Jack Coats" <j...@coats.org>: > > > > If that is the case, it should be great for 'i just erased my last weeks > work' problem, but disaster recovery would be a issue (or for any non-flat > file recovery, like databases that are backed up 'live' rather than exports > being backed up). > > I guess I'm missing the point here, but in the case of the 'live' > databases; how is that different? > > Isn't that restore case always the same? Or should I think more along the > lines of feeding the data back to the dbms and let the software itself care > about storing the data? > > Mvg, Guus Snijders > (Who just saw another learning opportunity) > -- ><> ... Jack The Four Boxes of Liberty - "There are four boxes to be used in the defense of liberty: soap, ballot, jury and ammo. Please use in that order." "Whatever you do, work at it with all your heart"... Colossians 3:23 "Anyone who has never made a mistake, has never tried anything new." - Albert Einstein "You don't manage people; you manage things. You lead people." - Admiral Grace Hopper, USN "The most dangerous phrase in the language is "We’ve always done it this way"-- Admiral Grace Hopper, USN "Tell me and I forget. Teach me and I remember. Involve me and I learn." - Ben Franklin
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