Specifies the number of weekly, nightly, and hourly Snapshot copies to keep on the storage system.
The following list describes the default values for when the different Snapshot copies are taken:
Weekly Snapshot copies are taken at 24:00 on Sunday, creating Snapshot copies called weekly.n, where n is an integer (weekly.0, weekly.1, weekly.2, and so on).
Nightly Snapshot copies are taken at 24:00 Monday through Saturday, creating Snapshot copies called nightly.n, where n is an integer (nightly.0, nightly.1, and so on).
Four hourly Snapshot copies are taken at 8 a.m., noon, 4 p.m., and 8 p.m., unless specified otherwise using the hourly Snapshot copy schedule in this window, creating Snapshot copies called hourly.n, where n is an integer (hourly.0, hourly.1, hourly.2, and so on).
The storage system creates only one Snapshot copy at a time. For example, when it is creating the weekly Snapshot copy at 24:00 on Sunday, it does not create the hourly or nightly Snapshot copy at that time.
By default, Data ONTAP retains the two most recent nightly Snapshot copies and the six most recent hourly Snapshot copies, and deletes the oldest nightly and hourly Snapshot copies when new Snapshot copies are created. The following guidelines provide information about how to decide the number of Snapshot copies to keep:
If users rarely lose files or typically notice lost files right away, use the default Snapshot copy schedule.
If users commonly lose files and need to restore them, delete the Snapshot copies less often than specified by the default schedule.
For file systems that change very quickly, reduce the number of Snapshot copies scheduled. For example, if the entire file system is filled and emptied each day (for example, a file system storing large temporary files for a CAD application), it might not be appropriate to use daily or weekly Snapshot copies. On a very active system, schedule Snapshot copies every hour and keep them for just a few hours.