On Mon, Jan 06, 2003 at 12:48:22PM -0500, Casey Duncan wrote:
As for restoration, FileStorage is pretty resilient to data loss due to the fact that it only appends transactions to the file.
The last time this subject came up, there was a quibble about this that made me perhaps overly cautious about assuming the above is true. I've dug it out of the archives and read it more closely now. Summary: NORMALLY zope & FileStorage only append to the file, but it is conceivable that a third-party Zope product might alter this. I don't know which, if any, Products actually do this. Here's the message from the zope@zope.org archive: Toby Dickenson wrote:
On Monday 28 October 2002 1:41 am, Jens Vagelpohl wrote:
FileStorage only appends at the end of the file.
Not entirely true. FileStorage still supports a non-transactional undo mechanism that writes bytes to the middle of files. This mechanism is not normally used by Zope, however it might be used by other non-Zope ZODB applications, or custom products.
(could it be exploited by an attacker who wanted to break your backups? hmmmm)
Proviing that this type of live backup is safe requires knowledge about how the backup program will read the file. The obvious approach of reading from start to end is compatible with FileStorages append-only approach, but not all backup programs operate that way. I prefer to take a copy of the data.fs using 'cp' (which I know to be safe), and backup that.
-- Paul Winkler http://www.slinkp.com Look! Up in the sky! It's THE CROTCH! (courtesy of isometric.spaceninja.com)