[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]

Re: [linux-lvm] Snapshots and mmaped files.



I don't think this is an issue of the database needing to be quiescent. The problem I'm seeing is that when the application modifies the database _after_ the snapshot is taken, the modifications partially appear in the snapshot as well. I'm guessing that file modification that goes through write does the right thing in the snapshot, but modifications done via mmap don't cause the snapshot to duplicate the data.

The Berkely DB code should be able to recover from a coherent snapshot taken at any point in time.

Dave

On Wed, 20 Apr 2005 14:36:19 -0700, Dan Stromberg <strombrg dcs nac uci edu> wrote:

If lvm2 snapshots are like most snapshots, then they aren't a panacea -
they only decrease the window during which your database must be
quiescent.

EG, with snapshotting:

1) Shut down database
2) bifurcate off a snapshot
3) Start up database
4) Do backup against snapshot
5) Eliminate snapshot


EG without snapshotting:


1) Shut down database
2) Do backup
3) Start up database


The first case has more steps, but it also has a lot shorter time during which your database is inactive.


[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]