Note:

• If there is at least one connected iSCSI session associated with the LUN and is used by Windows Server or VMware ESXi Server, we recommend installing the Synology Snapshot Manager plug-in to avoid possible data inconsistencies. Otherwise, you must stop any applications and log off these sessions from the initiators before proceeding.
• LUN snapshot, restore and clone functions are only available on iSCSI LUNs with storage acceleration commands.
• If you took a snapshot or created a clone, and the status turned out to be Abnormal/Crashed, please delete this snapshot/clone and create another one.
• All changes to a LUN after a snapshot was created will be lost when you restore LUN to this snapshot.
• The functions including restoring iSCSI LUNs, cloning iSCSI LUNs, and taking and cloning iSCSI LUN snapshots are not available when a volume has less than 1GB of free space.

Retention Policy

This option provides an ideal solution to help you specify the maximum amounts of snapshot versions to save your volume space, but you may need to retain your snapshots for longer periods of time. There are a few things to note about Retention Policy:

• Synology employs the GFS, or Grandfather-Father-Son retention policy. You can configure the maximum amounts of snapshot versions to be retained for the following time ranges respectively: hourly, daily, weekly, monthly, and yearly.
• One snapshot can meet several retention rules at the same time. For example, one snapshot can meet the daily, weekly, and monthly rules.
• The earliest snapshots will be retained if you take many snapshots within a certain period. For example, if you set a 10 weekly snapshots retention rule, and your snapshot schedule is set to take 1 snapshot a day, Snapshot Replication will retain the earliest snapshot of each week for the past 10 weeks.
• If you have not taken snapshots for a certain period, the system will retain the most recent snapshots. For example, if the daily snapshot rule is set as 15 and there were not any snapshots taken in the past 30 days, the system will retain the snapshots taken 30 to 45 days ago.
• All snapshot versions within one hour since the taking of newest snapshot will be kept by default, for your convenience to find and restore from recent snapshot versions. You can also lock a snapshot to prevent it from automatic removal by your retention rules.

Example 1:
If you want to keep daily snapshots for the past 3 months, weekly snapshots for the past 4 to 6 months, and monthly snapshots for the past 7 to 9 months, you need to input 0 for hourly snapshots, 90 for daily snapshots, 24 for weekly snapshots, 9 for monthly snapshots, and 0 for yearly snapshots.

Example 2:
If you want to keep hourly snapshots for the past 2 days, daily snapshots for the past week, weekly snapshots for the past month, and monthly snapshots for the past year, you need to input 48 for hourly snapshots, 7 for daily snapshots, 4 for weekly snapshots, 12 for monthly snapshots, and 0 for yearly snapshots.