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'APFS now support snapshots, a feature users of Virtual Machines love and can barely live without!' Why is this especially useful for VM lovers ?

by Gys 9y ago

hamandcheese 9y ago
I don't think its "especially useful" for them, just the most likely place end users are exposed to snapshots.
- wila 9y ago
  Yes ^^ this ^^, virtual machines have been a good way to learn how useful and easy snapshots are. With APFS snapshots have come to the hardware level and that is really exciting. But beware that this is not a backup. If you loose your main disk then you still might have lost your data. Time machine can help very well here. Regular TM backups are a good way of protecting yourself against data loss. Unless.. we're talking VMs again. In that particular scenario it turns out that VMs and Time Machine do not go that well together. VMware even advices you to exclude your virtual machines from VMs [0] and [1]. The problem is that your VM consists of large binary files that change over time. If TM makes a backup it will always see your VM as changed and start copying the virtual disk files. Problem is that if the machine is running that the risk is high that you end up with corrupt virtual disks in your time machine. Another problem is that if your TM backup storage runs out of storage space. TM can delete part of your virtual disks. Another problem is that with VMs you run out of disk space really quick. Anyways I'm getting off topic. Probably because I wrote Vimalin [2] to backup VM's for VMware Fusion and counter the VM backup issues ;) [0] https://kb.vmware.com/kb/1013628 https://kb.vmware.com/kb/1013628 [1] https://docs.vmware.com/en/VMware-Fusion/10.0/com.vmware.fusion.using.doc/GUID-644C040A-0831-483F-9A06-EE970C2F9FF6.html https://docs.vmware.com/en/VMware-Fusion/10.0/com.vmware.fus... [2] https://www.vimalin.com https://www.vimalin.com
  - walterbell 9y ago
    How does Vimalin backup in-use virtual disks, or deal with the large binary files that have only small differences?
    - wila 9y ago
      It depends on VMware Fusion snapshot functionality. As such it is not a problem to make backups of a running virtual machine. The way it works is that it makes a temporary snapshot of the VM when it is running. Parts of the disk from before the snapshot are now closed and new data is written as Copy on Write. The data that is safe to copy (which includes your VM state and memory) is then copied to your backup location. After Vimalin is finished copying the data it will also commit that temporary snapshot. On restoring a backup it gets back to the state from before the backup started, just like with a snapshot, except this was written on an external disk. You can schedule when it is convenient for you to run the backups. Like Time Machine it makes full copies of the disks. But because you can schedule how many copies you want to keep you can prevent your backup storage from getting overrun.
jlgaddis 9y ago
I run lots of stuff in VMs because I want to experiment or because I'm not sure if something's going to work right. It's nice to just take a snapshot and then do whatever task you wanted to do. If everything gets screwed up, it's no big deal. Just roll back to that last snapshot you made and start over. I do the same thing on my FreeBSD machines when installing updates (thanks to ZFS).
heywire 9y ago
Snapshots are a huge timesaver for me. I work on a large legacy windows application where it might take me an hour to set up the system in such a way to reproduce an issue. I can do that once, then revert to that snapshot over and over while debugging the issue. They also save a ton of time when performing upgrades (reverting on failure) or when I need to load a customers configuration files. I spend most of my day in VMWare workstation and use snapshots almost every day.
Someone 9y ago
If you accidentally change or delete a file from a file system, it is fairly fast to roll back that change by restoring that file from backup. If you accidentally change or delete a file from a file system on a VM image, rolling back the change means restoring the entire VM image from backup. That may mean a multi-GB restore, even if the file is only a few kB (rsync won’t help much, as it still would require you to read the entire backup and the entire changed VM image) With a COW snapshot, rolling back that accidental change can be even faster than restoring the file from backup, as it only means changing some on-disk pointers (of course, you would still need the backup, as that COW snapshot isn’t a backup; it would die if your disk died)

'APFS now support snapshots, a feature users of Virtual Machines love and can barely live without!' Why is this especially useful for VM lovers ?

by Gys 9y ago

'APFS now support snapshots, a feature users of Virtual Machines love and can barely live without!' Why is this especially useful for VM lovers ?

hamandcheese 9y ago

I don't think its "especially useful" for them, just the most likely place end users are exposed to snapshots.

wila 9y ago
Yes ^^ this ^^, virtual machines have been a good way to learn how useful and easy snapshots are. With APFS snapshots have come to the hardware level and that is really exciting. But beware that this is not a backup. If you loose your main disk then you still might have lost your data. Time machine can help very well here. Regular TM backups are a good way of protecting yourself against data loss. Unless.. we're talking VMs again. In that particular scenario it turns out that VMs and Time Machine do not go that well together. VMware even advices you to exclude your virtual machines from VMs [0] and [1]. The problem is that your VM consists of large binary files that change over time. If TM makes a backup it will always see your VM as changed and start copying the virtual disk files. Problem is that if the machine is running that the risk is high that you end up with corrupt virtual disks in your time machine. Another problem is that if your TM backup storage runs out of storage space. TM can delete part of your virtual disks. Another problem is that with VMs you run out of disk space really quick. Anyways I'm getting off topic. Probably because I wrote Vimalin [2] to backup VM's for VMware Fusion and counter the VM backup issues ;) [0] https://kb.vmware.com/kb/1013628 https://kb.vmware.com/kb/1013628 [1] https://docs.vmware.com/en/VMware-Fusion/10.0/com.vmware.fusion.using.doc/GUID-644C040A-0831-483F-9A06-EE970C2F9FF6.html https://docs.vmware.com/en/VMware-Fusion/10.0/com.vmware.fus... [2] https://www.vimalin.com https://www.vimalin.com
- walterbell 9y ago
  How does Vimalin backup in-use virtual disks, or deal with the large binary files that have only small differences?
  - wila 9y ago
    It depends on VMware Fusion snapshot functionality. As such it is not a problem to make backups of a running virtual machine. The way it works is that it makes a temporary snapshot of the VM when it is running. Parts of the disk from before the snapshot are now closed and new data is written as Copy on Write. The data that is safe to copy (which includes your VM state and memory) is then copied to your backup location. After Vimalin is finished copying the data it will also commit that temporary snapshot. On restoring a backup it gets back to the state from before the backup started, just like with a snapshot, except this was written on an external disk. You can schedule when it is convenient for you to run the backups. Like Time Machine it makes full copies of the disks. But because you can schedule how many copies you want to keep you can prevent your backup storage from getting overrun.

jlgaddis 9y ago

I run lots of stuff in VMs because I want to experiment or because I'm not sure if something's going to work right. It's nice to just take a snapshot and then do whatever task you wanted to do. If everything gets screwed up, it's no big deal. Just roll back to that last snapshot you made and start over. I do the same thing on my FreeBSD machines when installing updates (thanks to ZFS).

heywire 9y ago

Snapshots are a huge timesaver for me. I work on a large legacy windows application where it might take me an hour to set up the system in such a way to reproduce an issue. I can do that once, then revert to that snapshot over and over while debugging the issue. They also save a ton of time when performing upgrades (reverting on failure) or when I need to load a customers configuration files. I spend most of my day in VMWare workstation and use snapshots almost every day.

Someone 9y ago

If you accidentally change or delete a file from a file system, it is fairly fast to roll back that change by restoring that file from backup. If you accidentally change or delete a file from a file system on a VM image, rolling back the change means restoring the entire VM image from backup. That may mean a multi-GB restore, even if the file is only a few kB (rsync won’t help much, as it still would require you to read the entire backup and the entire changed VM image) With a COW snapshot, rolling back that accidental change can be even faster than restoring the file from backup, as it only means changing some on-disk pointers (of course, you would still need the backup, as that COW snapshot isn’t a backup; it would die if your disk died)