> From: Adam Levin [mailto:levi...@gmail.com] > > VMWare Tools allows VMWare to tell > the VM, through VSS, to quiesce, and then VMWare can take its snapshot -- > it knows to quiesce when it takes its own snapshot. Once that snapshot > exists, it's 100% safe
Actually, this is incorrect. In order for quiescing to do anything at all, an application must register with VSS as a writer. There may be some applications out there, that register as VSS writers, but don't provide crash consistency without VSS. You might gain some consistency in those cases, by quiescing, but it's only a marginal gain over snapshotting without quiescing, and it's definitely not correct to assume it's 100% guarantee with quiescing. With or without quiescing, the filesystem itself will be 100% consistent, and the ACID databases will be 100% consistent, but let's imagine some application was recording audio from a microphone and that application will stream 5 KB/sec to a file indefinitely. Then with or without quiescing, if the system rolls back, the file will be truncated, and may not be a valid mp3 file (or whatever). The only way you can have a 100% guarantee about all your files is to gracefully shutdown the VM and then snapshot, but nobody wants to do that. In reality, the risk of online snapshotting, with or without quiescing, are manageable. _______________________________________________ Tech mailing list Tech@lists.lopsa.org https://lists.lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
