VSS & Snapshots on virtual clients with Hyper-V on CSV
I need a better understanding on snapshots and writers on a Hyper-V backup scenario (CSV with 4 nodes - single policy). As far as i know.
- Netbackup is installed on the Hyper-V Hosts (nodes)
- Logs are created on the Hyper-V hosts.
- Network traffic is between Master-Media and Hyper-V Host
And according to the 7.5 Hyper-V Admin Guide - Phase 3:
The VSS Hyper-V writer quiesces the Windows virtual machine and creates the snapshot on the host volume. If the Hyper-V writer cannot quiesce the virtual machine, the virtual machine is placed in the Saved state before creation of the snapshot.
But, when you get an snapshot error (156) troubleshooting is on the virtual machine, according to this article:
To be specific, i mean:
- Enough space on each volume of the virtual machine.
- NTFS shadow storage on each/same volume of the virtual machine.
Those 2 issues must be checked on the virtual machine.
Last week i made a recomendation - (before being included in our Hyper-V backup) - to check if our new virtual machines had those configurations correct in order to avoid any CSV issues due the snapshots failing, and when our IT admin asked "why on the virtual machine, if everything happens in the host? makes no sense and nothing should be checked on the virtual machine, just the Hyper-V Hosts"
I couldn´t answer that question. I know for sure the technote is valid, because i´ve troubleshooted 156 error many times and always is due to no space on the virtual machine or NTFS shadow storage on different volumes. On the other hand, when backup is running, you can only list writers on the Hyper-V hosts,
I´m pretty sure this is something conceptual related to the VSS writer, and how snapshots are done. Would be nice if someone could explain me what i´m missing to understand.
Thanks a lot!