On Monday, 07/24/2006 at 06:35 ZE2, Carsten Otte <[EMAIL PROTECTED]> wrote: > > But rather than focus on that "edge" condition, we are all, I think, in > > violent agreement that you cannot take a volume-by-volume physical backup > > from outside a running Linux system and expect to have a usable backup. > That is a wrong assumption, I clearly disagree with it. If planned > proper, and I agree that there are lots of things one can do wrong > when planning the setup, physical backup of mounted and actively used > volumes _is_ reliable.
But you are making assumptions about the applications, something I am not willing to do quite yet. If a database update requires a change to the data file, the index file, and the log file, how do you (from the outside) know that all changes have been made and that it is safe to copy them? And that another transaction has not started? >From my days as a database application developer, a the transaction journal was meant to be replayed against a copy of the database as it existed at when the database was started, not replayed against a more current snapshot. I.e. today's log is replayed against last night's backup. And the transaction log is specifically NOT placed on the same device as the data itself. In Linux terms, I guess that means don't place it in the same filesystem since that's the smallest consistent unit of data, right? If you lose the data device, you haven't lost a whole day's worth of transactions. (Maybe database technology no longer requires such precautions?) So I'll admit that I'm obviously not "getting it". If you would summarize the steps needed to allow a reliable, usable, uncoordinated live backup of Linux volumes, I for one would sincerely appreciate it. How do you integrate them into your server? How do you automate the process? Right now I'm a fan of SIGNAL SHUTDOWN, FLASHCOPY, XAUTOLOG, but that's just me... Please be patient with me while I learn. :-) Alan Altmark z/VM Development IBM Endicott ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
