Hi Marcelo, > > On 05/05/2010 03:11 PM, Dean Hildebrand wrote: > > Right now, in order to quiesce the Guest OS file systems it is required to > > take a VM snapshot. We would like to avoid taking this snapshot for > > several reasons, most importantly disk space and performance. > > Are those the only things you want to avoid? > > For disk space, quiesced snapshots don't include memory information, so you > don't pay the largest cost of snapshots (the memory state file). The > delta disks > created are not large.
I guess that is true as long as you quickly delete the snapshot and don't let the delta file grow? > > For performance, there is a performance penalty, yes, but it's much lower than > having to keep your VM's disks frozen while you make a copy of the whole vmdk > file. With the snapshot, you can take as long as you want to copy the original > vmdk file since the VM won't be modifying it, and the VM can still > be alive and > kicking (since it will be writing to the delta disk). > > Then after you backup the vmdk you can delete the snapshot and solve > both problems. Yeah, that would be true if we were planning on copying the vmdk file. But our goal is to snapshot it in our file system (we are using a NFS data store to our file system), which is basically instantaneous. We've also heard people complaining about the 'stun' that occurs when you delete the snapshot. I assume this 'stun' is relatively minor when you only have a single snapshot, and the delta file doesn't grow too large, but it would still be nice to avoid altogether. > > > I've looked into the vmsync module, and it looks like we could manually > > call the ioctl to freeze/thaw the file systems. Has anyone tried this > > before? Do people think it would work with ESX 4? > > You could do that, but I'd really encourage you to just use regular snapshots > since it will be a lot safer. Safety wise, what are your major concerns? Once the VM file systems are frozen, all data will reside on the NFS server, so isn't it safe to assume that the data in the vmdk file on the NFS server is file system consistent? > > Also, since 2.6.29, the vanilla Linux kernel already supports ioctls that do > pretty much the same thing as vmsync does (for all filesystems, not > just XFS as > it previously did), without the need for our kernel driver. Yes, I recently found out about that addition to the Linux kernel. This means it will be in Rhel 6, which will be nice. Either way, if we do end up going down this path, it would be nice to be able to use the vstorage api's (VADP) to quiesce the VM file systems instead of having to access the VMs ourselves. It would seem like a big benefit to customers to enable back-end storage systems to provide file-system consistent backup facilities without experiencing the overhead of VM snapshots. (just my 2 cents). Thanks, Dean ------------------------------------------------------------------------------ _______________________________________________ open-vm-tools-devel mailing list open-vm-tools-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/open-vm-tools-devel
