We use the BlobStorage account storage3 for retention.
Storage lifecycle management offers a rule-based policy that you can use to transition blob data to the appropriate access tiers or to expire data at the end of the data lifecycle.
Note: Enable flow logging for IP traffic from VM5 and retain the flow logs for a period of eight months.
Reference:
https://docs.microsoft.com/en-us/azure/storage/blobs/lifecycle-management-overview
https://docs.microsoft.com/en-us/azure/network-watcher/network-watcher-nsg-flow-logging-overview
