Re: How do the backup programs work
From: Nick Landsberg (hukolau_at_NOSPAM.att.net)
Date: 03/11/04
- Next message: mjt: "Re: Win4Lin on Knoppix?"
- Previous message: Christopher Browne: "Re: How do the backup programs work"
- In reply to: Christopher Browne: "Re: How do the backup programs work"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Date: Thu, 11 Mar 2004 22:19:14 GMT
Christopher Browne wrote:
> Quoth John-Paul Stewart <jpstewart@binaryfoundry.ca>:
>
[SNIP]
>>
>>In general, backing up a database is quite a different operation
>>from backing up a filesystem. Postgres, for example, recommends
>>stopping the database entirely before backing up the filesystem on
>>which it resides. Or if you must leave the database running, it is
>>recommended to back up the database seperately using 'pg_dump' (or
>>similar). Other databases have similar procedures.
>
>
> "Recommends" does not word things nearly strongly enough.
>
> The alternative, of "backing up database files but not bothering to
> stop the database," may be quite safely assumed to lead to an
> inconsistent, invalid, and downright useless backup. There is no
> value whatsoever in doing that sort of backup, because it is quite
> certain that it will be corrupt and that any attempt to use that
> backup will lead to disaster.
>
>
>>IOW, if you just backup the filesystem on which an active database
>>resides, you're quite correct in assuming that the database files
>>will be inconsitent (or possibly omitted if the backup system
>>noticed they were written to) and thus the alleged backup of that
>>database would be useless.
>
>
> This is more widely true than that; it is fair to say that if
> applications that use multiple files or that modify the contents of
> files are active while a backup is taking place, the backups of those
> files will be of dubious integrity.
Hmmm... curious. If I had been you, Christofor,
I would have repeated myself and said
"downright useless" and "lead to disaster"
rather than "of dubious integrity."
Murphy (of Murphy's Law fame) was an optimist.
The probability approaches one (certainty) that
the one backup which you absolutely need to
restore your system was made while multiple
files were being updated, the files referenced
each other, and you picked up the OLD version
of one file and the NEW version of the other.
>
> Database management systems are the most conspicuous (and
> pathological) case of this, but the same can be true for other
> applications that do a lot of "file fiddling."
-- Ñ "It is impossible to make anything foolproof because fools are so ingenious" - A. Bloch
- Next message: mjt: "Re: Win4Lin on Knoppix?"
- Previous message: Christopher Browne: "Re: How do the backup programs work"
- In reply to: Christopher Browne: "Re: How do the backup programs work"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Relevant Pages
|
