Put guests on two VLANs through a virtual switch, and prove a snapshot is not a backup

applied · 50 min · Objective 2.5

Task

Configure the hypervisor's virtual switch so two guests land on different VLANs by their virtual NIC settings alone, with no configuration inside the guests. Then demonstrate why a snapshot is not a backup: take a snapshot, export a real backup copy to separate storage, and show which survives the loss of the original disk file.

Steps

  1. Put guest A's virtual NIC in VLAN 10 and guest B's in VLAN 20 on the virtual switch. Give them addresses in the same subnet, and try to ping B from A. Save the hypervisor's VLAN settings and the ping to lab/vswitch/vlans.txt.
  2. Move guest B to VLAN 10, ping again, and append the result.
  3. Take a snapshot of guest A. Separately, shut it down and export or copy the whole VM to the separate backup folder. Record both in lab/vswitch/protection.csv with header copy,location,depends_on.
  4. Simulate losing the original storage: move guest A's original disk file (not the snapshot delta, not the export) to another folder where the hypervisor cannot find it. Try to revert to the snapshot, then try to import the export. Record each result in lab/vswitch/loss-test.txt as two lines, snapshot: ok or snapshot: failed, and export: ok or export: failed, each followed by what the hypervisor said.
  5. Move the original disk file back.

Verify

These checks run in a POSIX shell: Terminal on macOS or Linux, and on Windows Git Bash (it comes with Git for Windows) or WSL. A stock Windows PowerShell or Command Prompt has no awk or grep, so there the first line fails.

grep -Eic '100% packet loss|unreachable' lab/vswitch/vlans.txt
grep -Ec ' 0% packet loss' lab/vswitch/vlans.txt
awk -F, 'NR>1 {print $1" -> depends on "$3}' lab/vswitch/protection.csv
grep -Eic 'snapshot.*(fail|error|missing)' lab/vswitch/loss-test.txt
grep -Eic '(export|backup).*(ok|success|start|work)' lab/vswitch/loss-test.txt

The guests could not reach each other on different VLANs and could on the same one, with nothing changed inside them. The snapshot failed without its original disk, and the export did not, because it was an independent copy on separate storage.

Notes

The same holds for storage array snapshots: useful for fast rollback, lost with the array. A snapshot becomes backup-grade only when it is replicated to independent storage, which the backup lessons return to.

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