David Boyes wrote: >> Therefore, dm-snapshot and >> flashcopy are two sides of the same medal once the entire filesystem >> is on a single dasd. > > That's a pretty large assumption, especially since the recommended > wisdom for most "advanced applications" -- like DB/2 and WAS -- is *not* > to put things like data and logs on the same filesystem for performance > reasons. Yup, I know that "everything on a single dasd" is a strong limitation. But since flashcopy does'nt allow to snapshot multiple volumes at a time, it is the only way to get a snapshot of all data involved from outside the system that I know of.
>> The point is, that data is considered stable at any time. That's a >> basic assumption which is true for ext3 and most applications. If you >> run a file system or an application that does have inconsistent data >> from time to time, you are in trouble in case of a power outage or >> system crash. I hope this is not the case in any production > environment. > > With respect, I think this is an unrealistic expectation. I don't > control the application programmers at IBM or S/AP or Oracle, etc. If > you want to preach on proper application design to those folks, I'll > happily supply amens from the pews, but out here in the real world, it > ain't so, and it ain't gonna be so for a good long while (or at least > until the current crop of programmers re-discover all the development > validation model work that we did back in the 70s at PARC). It depends on the type of application. For a fileserver or static webserver for example, this requirement is fullfilled. For more complex servers, it can get nasty. > With *today's* applications, you need a guaranteed valid state both from > the application *and* filesystem standpoint, and to get that, you need > to coordinate backups from both inside and outside the guest if you want > to use facilities outside the guest to dump the data. How you do that > coordination is what I think you're trying to argue and there, your > points are extremely valid and useful; my point still stands that > without coordination between Linux and whatever else you're using, > you're not going to get the desired result, which is a no-exceptions way > to handle backup and restore of critical data in the most efficient > manner available. Some people seem to trust today's applications more, for example the developers of dm-snapshot and the users of per-file backup soloutions like tsm which usually also run while the application is active. with kind regards, Carsten ---------------------------------------------------------------------- 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
