|Subject||RE: [firebird-support] Firebird backup on virtual machine|
> > My biggest concern was that after restore form Veeam backup firebirdVeeam uses a feature of the VMWare hypervisor that creates snapshots of the VMs virtual disk when a backup begins, so it is the hypervisor (Hyper-V has similar facility) creates that 'frozen' image of the database disk.
> > database file could be damage. If not there is nothing I can worry
> > about. I'm just want to be sure that when someone restore full vmdk
> > file my system will work and survive such operation.
> Unless Veeam works some magic that stops writes to the database while it
> makes its copy, there is a risk that the copy will not reflect the state of the
> database at any one instant.
The technique is similar to how nbackup works, it has the engine create a new file to which all new disk writes are written to...
In reality, in needs to be understood that the Windows file system operates like a transactional database, with snapshots representing disk "transactions". The only difference is that VSS has the ability to tag some transactions for historical references (think system restore points) and does not automatically merge/garbage collect the data from previous transactions.
Application require "VSS awareness" when the application does not use a careful disk write approach. Application register with the OS to be notified that a disk snapshot is has been requested (and when it is completed), so the application can ensure that the file on disk is 'logically correct ' for the current disk transaction.