Your data will stay untouched during the update. The only thing that you may to do is to restore the settings and configuration. It may be also needed to recreate the shares that will point to the directories on your NAS logical volumes.
It's hard to say what have happened to backup mechanism without seeing the logs.
As an alternative way you can copy the data to a host machine.
By the way there is no possibility to make backups of whole logical volumes, you can backup only specified shares.
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