I hate to beat a dead horse, but searching for "crash consistent" in the manual also finds this:
"VMFS also features enterprise-class crash consistency and recovery mechanisms, such as distributed journaling, a crash consistent virtual machine I/O path, and machine state snapshots. These mechanisms can aid quick root-cause and recovery from virtual machine, physical host, and storage subsystem failures." This specifically says that snapshots are a crash-consistent mechanism. That is the nice way of saying that they're the same as if you powered off the machine (i.e. it crashed). Again, they will work 99.9% of the time, but don't expect your application to be happy. It SHOULD recover from a crash, like they're supposed to do, but... --- W. Curtis Preston Backup Blog @ www.backupcentral.com VP Data Protection, GlassHouse Technologies > -----Original Message----- > From: Curtis Preston > Sent: Thursday, February 28, 2008 10:38 AM > To: Curtis Preston; Steven Kurylo; [email protected] > Subject: RE: Backing up VMware-VMs > > Here's some further information from the VMware manuals. I searched for > the word snapshot in all manuals here: > http://pubs.vmware.com/vi35/wwhelp/wwhimpl/js/html/wwhelp.htm > > > > First, you CAN take a snapshot of a powered-off machine. From the manual: > "You can take a snapshot while a virtual machine is powered on, powered > off, or suspended. If you are suspending a virtual machine, wait until the > suspend operation has finished before taking a snapshot. You must power > off the virtual machine before taking a snapshot if the virtual machine > has multiple disks in different disk modes." > > Also: > Note Snapshots of raw disks, RDM physical mode disks, and independent > disks are not supported. > > Also from the manual: > "When you take a snapshot, be aware of other activity going on in the > virtual machine and the likely effect of reverting to that snapshot. In > general, it is best to take a snapshot when no applications in the virtual > machine are communicating with other computers. The potential for problems > is greatest if the virtual machine is communicating with another computer, > especially in a production environment. > > For example, if you take a snapshot while the virtual machine is > downloading a file from a server on the network, the virtual machine > continues downloading the file, communicating its progress to the server. > If you revert to the snapshot, communications between the virtual machine > and the server are confused and the file transfer fails. Another example > is taking a snapshot while an application in the virtual machine is > sending a transaction to a database on a separate machine. If you revert > to that snapshot-especially if you revert after the transaction starts but > before it has been committed-the database is likely to be confused." > > This does not sound like I don't have to worry about the state of my > machine while taking a snapshot. > > --- > W. Curtis Preston > Backup Blog @ www.backupcentral.com > VP Data Protection, GlassHouse Technologies > > > -----Original Message----- > > From: [EMAIL PROTECTED] [mailto:owner-amanda- > [EMAIL PROTECTED] > > On Behalf Of Curtis Preston > > Sent: Thursday, February 28, 2008 10:21 AM > > To: Steven Kurylo; [email protected] > > Subject: RE: Backing up VMware-VMs > > > > After consulting with two VMware experts, I stand by my original > > statement, that a snapshot of a vm is a crash consistent copy, which > > means that it's just like someone pulled the power plug. It is NOT like > > someone suspending a VM. > > > > There are 3rd party products that provide additional levels of > > consistency (netapp, falconstor that I know of), but the default VMware > > snapshots are crash consistent, not transactional consistent. > > > > --- > > W. Curtis Preston > > Backup Blog @ www.backupcentral.com > > VP Data Protection, GlassHouse Technologies > > > > > -----Original Message----- > > > From: Steven Kurylo [mailto:[EMAIL PROTECTED] > > > Sent: Wednesday, February 27, 2008 2:06 PM > > > To: Curtis Preston; [email protected] > > > Subject: Re: Backing up VMware-VMs > > > > > > Curtis Preston wrote: > > > > Unless you're coordinating with the OS, then taking a VMware > > snapshot > > > > and copying it is equivalent to pulling the power plug on a server. > > > > Will it power back up without corruption? 99.9% of the time, yes. > > Has > > > > anyone who has been in the biz for a while had a scenario where > > > > powercycling a box caused a corrupted OS disk? I'd say so. > > > > > > > Thats false. > > > > > > Its the same thing as suspending a VM. When you restore the you can > > > either restore it as if the power was shut off or resume it as if > > > nothing had happened. Obviously the outside world has changed, so > > > network connections, the time, etc, will have changed.
