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Backup Operations in Hyper-V -
No VSS Writer Available?
In some cases, you need an Application-consistent backup but there is no VSS writer available. One example of this is MySQL. Hyper-V backups of virtual machines containing MySQL will always result in either a crash consistent or an image-level backup. For MySQL, the latter is probably acceptable as MySQL doesn't perpetually expand the log file. However, if you're using MySQL within a VSS-aware VM, then a Hyper-Vbased backup tool is going to take a crash- consistent backup. MySQL (like any other database system) isn't always recoverable from a crash-consistent backup; tool is going to take a crash-consistent backup. MySQL (like any other database system) isn't always recoverable from a crash-consistent backup; even when recovery is possible, it may be painful.
MySQL is just one example; any number of line-of-business Applications could tell a similar tale. In the case of MySQL, one solution is to find a guest-level backup
Application that is MySQL- aware and can back it up properly. For Applications for which no backup Application has a plug-in, you may need to have pre- and post-backup scripts that stop services or close Applications. If brief downtime is acceptable, you can disable the Backup item in Hyper-V Integration Services, thereby forcing Hyper-V to save the state of the VM during backup. This technique results in an image-level backup and can be used on any Application that doesn't have a VSS writer.
References:
https://www.altaro.com/hyper-v/vss-crash-consistent-vs-application-consistent-vss-backups-post-2-of-2/
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