OK. From discussion above, can we reach a conclusion: from the application perspective, it is very hard, if not impossible, to take a transactional consistent snapshot without the help from applications? Chris, you mentioned that "Many different applications support some form of pausing in order to facilitate live backups. " Can you provide some examples? I mean popular apps. Finally, if we back up a little bit, say, we don't care the transaction level consistency ( a transaction that open/close many times), but we want a open/close consistency in snapshots. That is, a file in a snapshot must be in a single version, but it can be in a middle state of a transaction. Can we do that? Pausing apps itself does not solve this problem, because a file could be already opened and in the middle of write. As I mentioned earlier, some systems can backup old data every time new data is written, but I suspect that this will impact the system performance quite a bit. Any idea about that? Thanks. On 7/3/07, Chris Mason <chris.mason@xxxxxxxxxx> wrote:
On Tue, 3 Jul 2007 12:31:49 -0400 "Xin Zhao" <uszhaoxin@xxxxxxxxx> wrote: > That's a good point! > > But this sounds hopeless to take a real consistent snapshot from app > perspective unless you shutdown the computer. Right? Many different applications support some form of pausing in order to facilitate live backups. You just have to keep it all in mind when designing the total backup solution. -chris
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