Knowledge Center

Snapshot

To take a LUN snapshot:

A snapshot of a LUN is a point-in-time, read-only copy of a LUN.

  1. Select the LUN of which you want to take snapshots.
  2. Click Snapshot and choose Take a Snapshot.
  3. Enter a description for this snapshot.
  4. Choose whether to enable the following options:
    • Lock: Select this checkbox to prevent this snapshot from being automatically deleted by the retention policy.
    • Immutable snapshots: Select this checkbox to prevent this snapshot and the LUN it belongs to from being deleted. We recommend setting the protection period to between 7 and 14 days.
      Note: Once the Immutable snapshots checkbox is selected, you cannot unselect it. This option will be automatically unselected by the system when the protection period ends.
  5. Choose either of the following snapshot types according to your needs:
    • Application consistent: This type of snapshot can only be taken when Synology Storage Console is installed on your Windows server or VMware vCenter Server depending on your operating environment to communicate with DSM. When application-consistent snapshots are triggered on DSM, applications will be notified and flush all the data from memory to the LUN on which the snapshot is taken to guarantee data consistency.
    • Crash consistent: If no Synology Storage Console is installed on either of your clients, you can only capture crash-consistent snapshots of LUNs. When they are triggered, applications will not be notified to flush the data from memory to the LUN and therefore guarantee no data consistency.
  6. Click OK.

Note:

  • You are highly recommended to install Synology Storage Console to avoid possible data inconsistencies.

Terminology:

  • Synology Storage Console: Synology Storage Console is a storage management plugin on VMware vSphere Client or Windows Server that simplifies managing and monitoring multiple Synology storage systems. It also allows you to take application-consistent snapshots directly from DSM.

To delete a snapshot:

  1. Select a LUN that you took snapshots for.
  2. Click Snapshot > Snapshot List.
  3. Select the snapshot you want to delete and click Remove.

Note:

  • Space reclamation takes time to process after snapshots are deleted.

To restore a LUN:

Select a point-in-time snapshot to restore the data on a LUN.

  1. Select the LUN you want to restore.
  2. Click Snapshot and choose Snapshot List.
  3. Select a snapshot to which you want to restore and click Restore.

To make a clone of LUN from snapshots:

Make a writable copy of LUN or LUN snapshot.

  • Select a LUN snapshot from Snapshot List and click Clone.

Note:

  • If there is at least one connected session associated with the LUN and is used by Windows Server or VMware ESXi Server, we recommend installing the Synology Storage Console 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 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 LUNs, cloning LUNs, and taking and cloning LUN snapshots are not available when a volume has less than 1 GB of free space.

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Retention Policy

Setting a retention policy helps you manage your storage space more efficiently by keeping the snapshots you want. There are three options for retention policies to choose from:

  • Numbers of latest snapshots to keep: Specify the number of the latest snapshots to retain.
  • Keep all snapshots for: Retain all snapshots taken within certain days.
  • Advanced retention policy: Snapshots can be kept for longer periods but your storage space can be saved at the same time.
    • You can set multiple rules and customize the retention policy according to your needs.
      • Retain all snapshots taken within certain days.
      • Advanced retention policy also allows you to keep the latest snapshots of different time frames for certain periods. You can choose how long the hourly, daily, weekly, monthly, and yearly snapshots will be retained in the system. For example, Keep the latest snapshot of the week for 7 weeks means that the last snapshot taken during a week will be retained for seven weeks after it is taken.
      • You will also need to set the Number of the latest snapshots to keep. If there are fewer snapshots than the specified number, the retention policy will not take effect. This is a required field.
    • Advanced retention policy employs the GFS, or Grandfather-Father-Son, retention mechanism.
    • A snapshot can meet more than one retention rule at a time. For example, a snapshot can be retained by the weekly retention rule and daily retention rule at the same time.

Example
It's October now and you have a snapshot schedule that takes one snapshot every day. If you are planning for a retention policy that covers the past nine months and want to keep

  • Daily snapshots for the first 3 months (September, August, and July)
  • Weekly snapshots for the 4th to 6th months (June, May, and April)
  • Monthly snapshots for the 7th to 9th months (March, February, and January)
  • 10 latest snapshots

you may refer to the following settings:

A snapshot can meet more than one retention rule. Therefore, the first weekly snapshot can also be the seventh daily snapshot, and the first monthly snapshot can also be the fourth weekly snapshot.

Setting the Number of latest snapshots to keep prevents the retention policy from deleting all snapshots when the system stops taking new snapshots, and the 10 latest snapshots will be the daily snapshots taken in the past 10 days.