On Sat, Feb 24, 2018 at 11:57:32PM +0100, Gionatan Danti wrote: > Il 24-02-2018 23:07 Dave Chinner ha scritto: > >Define "busy file", please. > > Think about a running virtual machine. Maybe an XFS-based virtual > image (ie: a CentOS 7 guest). > > >If the file is being actively written, then the clone will not be > >consistent. > > > >Yes, it's just like any other snapshot process - you have to quiesce > >everything that is writing to the file before cloning it. i.e. the > >data in the file needs to be in a stable, consistent, unchanging > >state if you want the clone to contain consistent data... > > About *what* level of consistency are we speaking? I understand that > application-level consistency requires a quiesced filesystem and, > possibly, an application-level agent. But is it a quiesced > filesystem a requisite for a *crash-consistent* ie: pull the plug) > snapshot? Yes, you have to freeze the filesystem to get a crash-consistent snapshot of the filesystem. > In other words: would a cp --reflink=always <vmdisk> <snapshot> of a > runnig virtual machine produce an usable, crash-consistent snapshot, > or it risks ending with binary garbage? You will end up with garbage. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
