Synology UC3200 is a dual-active IPSAN purpose-built for iSCSI services. With a shared storage design, the same drives are addressable by both controllers, reducing costs needed considerably when compared to an SHA cluster. Combine with other tools, such as Snapshot Replication, for a comprehensive backup strategy.
Dedicated IPSAN, UC3200
Converged NAS/IPSAN, SA3200D

Recovery Point Objective (RPO) is measured in time, of how much data is potentially lost based on the frequency of your backups.
Recovery Time Objective (RTO) is also measured in time, of how fast you are able to restore services after disruption occurs.

RPO and RTO are both important metrics in determining your backup strategy. A successful and cost-effective strategy requires you to understand what kind of data each backup task is protecting, and the importance of it.

For example, while family photos and videos are things you can't ever replace, you can probably accept a temporary inability to access them. For this, you will need a low RPO but can tolerate a high RTO.
For important legal or financial data, a company is going to want to achieve near-zero RPO and a reasonable RTO so that business activities can be resumed. When looking at data shares which are primarily used as cache, or scratch disks, such as for rendering or video production work, the data stored on there is trivial, while service availability may heavily impact productivity.

Hyper Backup can back up NAS data, applications and configurations with customizable frequency down to once an hour; for backed up data, administrators may set up version rotation policy to keep valuable historical versions and meet users' needs.

Synology Drive ShareSync is designed to synchronize data between two or more NAS servers whenever files are modified in monitored folders; however, to secure configuration and application backups, it's recommended to use Hyper Backup for protection.

While Cloud Sync encrypts data during transit, the data will be accessible to anyone that can access the public cloud account. Cloud Sync provides an optional client-side encryption capability that must be enabled to ensure the data is also encrypted at the destination.

Snapshot Replication: Replication of encrypted shared folders creates an unmounted encrypted folder, requiring the encryption key to access.

Hyper Backup: Client-side encryption protects the backup archives from unauthorized access, even if the public cloud account is compromised.

DSM is installed on each drive. Removing the original drives and replacing it with a new one will not help the original installation.

For 2-step verification:
Administrator users can only reset 2-step verification for other users.

To reset administrators' own 2-step verification, they need to reset DSM by pressing the RESET button on their Synology NAS servers.

For more information, please refer to this article

iSCSI Manager provides two types of space allocation for iSCSI LUNs, Thin Provisioning and Thick Provisioning.

Thick Provisioned LUNs are given the space they require upon creation, so despite you may be using only 2 GB out of the entire 10 GB on a LUN, the LUN still takes up 10 GB on the volume. Therefore, no matter how many files you delete, it will not decrease the space taken up by the LUN on the volume.

Thin Provisioning allows on-demand space allocation, which means that a Thin Provisioned LUN is taking up the storage space when it actually needs it. With space reclamation option enabled, the system is able to reclaim storage space after you delete data on Thin Provisioned LUNs, allowing you to utilize the free space for other purposes.

Hardware-assisted Zeroing is supported on both LUN types for better virtual disk initialization efficiency.

Virtual Machine Manager (VMM) when utilizing VM HA allows for a VM host to failover to the designated node. However, VMM has a 5-minute RPO when the primary storage node fails.

Synology High Availability (SHA) clusters constantly sync the active and passive nodes, ensuring RPO is kept nearly at zero. Minute-level RTO ensures that services can be quickly restored.

Btrfs protects data integrity; however, it is not for increasing security level of your NAS.

To increase NAS security, it's recommended to enable only HTTPS secure connection to the NAS. In addition, Synology helps keep your NAS safe from known vulnerabilities by providing DSM and package updates; make sure to be aware and follow the updates closely!

Learn more about the security measures in DSM.

Active Backup for Business supports changed block tracking to minimize the amount of data that needs to be backed up each time the task runs. This is similar to how snapshots only store the differences between versions.

The main benefit to ABB over datastore protection is the flexibility in protecting each VM with different policies, which would require creating a separate iSCSI LUN or shared folder if done through just snapshots or via Hyper Backup.

ABB additionally supports global deduplication, which can greatly increase storage efficiency.

ABB is able to protect VMs but is designed to operate locally with the hypervisor. A better approach would be to leverage ABB locally, then use Hyper Backup to send the backup repository to a remote NAS. At the remote site, the installation of ABB will be able to recover the backups and perform the restoration.