Creating snapshot schedules

About creating snapshot schedules

Data ONTAP provides a default snapshot schedule for each volume. You can configure the schedule to fit your needs. This schedule creates snapshots automatically and deletes old snapshots after a predetermined amount of time.

The default snapshot schedule

When you install Data ONTAP on a filer, it creates a default snapshot schedule. The default snapshot schedule automatically creates one nightly snapshot Monday through Saturday at midnight, and four hourly snapshots at 8 a.m., noon, 4 p.m., and 8 p.m. Data ONTAP retains the two most recent nightly snapshots and the six most recent hourly snapshots, and deletes the oldest nightly and hourly snapshots when new snapshots are created. You can see an example of the output for the default schedule in Default snap schedule command results.

User-specified snapshot schedules

There are three types of schedules that you can set up to run automatically using the snap sched command. The following table describes the three types.

Type	Description
Weekly	Data ONTAP creates these snapshots every Sunday at midnight. Weekly snapshots are called weekly.n, where n is an integer. The most recent weekly snapshot is weekly.0, and weekly.1 is the next most recent weekly snapshot.
Nightly	Data ONTAP creates these snapshots every night at midnight, except when a weekly snapshot is scheduled to occur at the same time. Nightly snapshots are called nightly.n, where n is an integer. The most recent nightly snapshot is nightly.0, and nightly.1 is the next most recent nightly snapshot.
Hourly	Data ONTAP creates these snapshots on the hour or at specified hours, except at midnight if a nightly or weekly snapshot is scheduled to occur at the same time. Hourly snapshots are called hourly.n, where n is an integer. The most recent hourly snapshot is hourly.0, and hourly.1 is the next most recent hourly snapshot.

Type

Description

Weekly

Data ONTAP creates these snapshots every Sunday at midnight.

Weekly snapshots are called weekly.n, where n is an integer. The most recent weekly snapshot is weekly.0, and weekly.1 is the next most recent weekly snapshot.

Nightly

Data ONTAP creates these snapshots every night at midnight, except when a weekly snapshot is scheduled to occur at the same time.

Nightly snapshots are called nightly.n, where n is an integer. The most recent nightly snapshot is nightly.0, and nightly.1 is the next most recent nightly snapshot.

Hourly

Data ONTAP creates these snapshots on the hour or at specified hours, except at midnight if a nightly or weekly snapshot is scheduled to occur at the same time.

Hourly snapshots are called hourly.n, where n is an integer. The most recent hourly snapshot is hourly.0, and hourly.1 is the next most recent hourly snapshot.

Note
When Data ONTAP creates a weekly, nightly, or hourly snapshot, the value of n is adjusted for all the weekly, nightly, or hourly snapshots. The higher the value of n, the older the snapshot.

Displaying the snapshot schedule

To display the snapshot schedule for a volume on a filer, complete the following step.

Step	Action
1	Enter the following command: *snap sched [volume_name]* Note If you do not specify a volume name, `snap sched` displays the snapshot schedule for each volume on the filer.

Example

The following is an example of the snap sched command output:

filerA>snap sched vol1

Volume vol1: 2 6 8@8,12,16,20

What the snap sched command arguments mean

The following illustration explains the arguments in a sample snap sched command output.

Snapshot schedule results

This schedule keeps the two most recent weekly snapshots, the six most recent nightly snapshots, and the eight most recent hourly snapshots, created at 8 a.m., noon, 4 p.m., and 8 p.m. every day. Whenever the snapshot schedule creates a new snapshot of a particular type, it deletes the oldest one and renames the existing ones. On the hour, for example, the filer deletes hourly.7, renames hourly.0 to hourly.1, and so on.

Note
If you omit the @ argument specifying the hours for the hourly snapshots, Data ONTAP creates a snapshot every hour. Nightly and weekly snapshots are always created at midnight.

Strategies for creating a snapshot schedule

Following are some strategies for scheduling and retaining snapshots:

If users rarely lose files or typically notice lost files right away, use the default snapshot schedule. This schedule creates no weekly snapshot; it creates a snapshot every night and keeps two; and it creates hourly snapshots at 8 a.m., noon, 4 p.m., and 8 p.m, and keeps six. Following is the default snapshot command:
```
snap sched volume_name 0 2 6@8,12,16,20 
```

If users commonly lose files or do not typically notice lost files right away, Network Appliance recommends that you delete the snapshots less often than you would if you used the default schedule.
Following is the recommended snapshot schedule for this situation. It keeps two weekly snapshots, six nightly snapshots, and eight hourly snapshots:
```
snap sched vol1 2 6 8@8,12,16,20 
```
On many systems, only 5% or 10% of the data changes each week, so the snapshot schedule of six nightly and two weekly snapshots consumes 10% to 20% of disk space. Considering the benefits of snapshots, it is worthwhile to reserve this amount of disk space for snapshots. For more information on how snapshots consume disk space, see Understanding snapshot disk consumption.

You can create different snapshot schedules for different volumes on a filer. On a very active volume, schedule snapshots every hour and keep them for just a few hours, or turn off snapshots. For example, the following schedule creates a snapshot every hour and keeps the last three:
```
snap sched vol2 0 0 3 
```
This schedule does not consume much disk space, and it lets users recover files in recent snapshots as long as they notice their mistake within a couple of hours.
When you create a new volume on a filer, the new volume inherits the snapshot schedule from the root volume. After you use the volume for a while, check how much disk space the snapshots consume and how often users need to recover lost files, and then adjust the schedule as necessary.

Changing the snapshot schedule

To change the automatic snapshot schedule for a specific volume, complete the following step.

Step	Action
1	Enter the following command: snap sched volume_name weekly nightly hourly@n,n,.... volume_name is the name of the specific volume for the snapshot. weekly is the number of weekly snapshots to keep. nightly is the number of nightly snapshots to keep. hourly is the number of hourly snapshots to keep. n,n,... specifies the hours at which to create the hourly snapshots. Note A zero in any of the three schedules (weekly, nightly, hourly) disables snapshots for that interval.

Step

Action

Enter the following command:

snap sched volume_name weekly nightly hourly@n,n,....

volume_name is the name of the specific volume for the snapshot.

weekly is the number of weekly snapshots to keep.

nightly is the number of nightly snapshots to keep.

hourly is the number of hourly snapshots to keep.

n,n,... specifies the hours at which to create the hourly snapshots.

Note
A zero in any of the three schedules (weekly, nightly, hourly) disables snapshots for that interval.

Default snap schedule command results

This is the default automatic snapshot schedule:

snap sched volx 0 2 6 @8,12,16,20

The following example lists the snapshots created using the default schedule (where January 11 is a Sunday):

ls -lu .snapshot

total 64

drwxrwsrwx  1 root 4096 Jan 14 12:00 hourly.0

drwxrwsrwx  1 root 4096 Jan 14 08:00 hourly.1

drwxrwsrwx  1 root 4096 Jan 13 20:00 hourly.2

drwxrwsrwx  1 root 4096 Jan 13 16:00 hourly.3

drwxrwsrwx  1 root 4096 Jan 13 12:00 hourly.4

drwxrwsrwx  1 root 4096 Jan 13 08:00 hourly.5

drwxrwsrwx  1 root 4096 Jan 14 00:00 nightly.0

drwxrwsrwx  1 root 4096 Jan 13 00:00 nightly.1

Note
Daily snapshots are created at midnight of each day except Sunday, and weekly snapshots are created at midnight on Sunday. Only one snapshot is created at a time. If a weekly snapshot is being created, for instance, no daily or hourly snapshot will be created even if one is scheduled.

Disabling and enabling automatic snapshots

You can disable automatic snapshots for a period of time without changing the automatic snapshot schedule.

To temporarily disable or enable automatic snapshots, complete the following step.

Step	Action
1	If you want to...	Then...
Disable automatic snapshots	Enter the following command: *vol options volume_name* nosnap on** volume_name is the name of the volume for which you want to disable automatic snapshots.
Enable automatic snapshots	Enter the following command: *vol options volume_name* nosnap off** volume_name is the name of the volume for which you want to enable automatic snapshots.

Step

Action

If you want to...

Then...

Disable automatic snapshots

Enter the following command:

vol options volume_name 
nosnap on

volume_name is the name of the volume for which you want to disable automatic snapshots.

Enable automatic snapshots

Enter the following command:

vol options volume_name 
nosnap off

volume_name is the name of the volume for which you want to enable automatic snapshots.

Note
You can also disable automatic snapshots by changing the snapshot schedule so that no snapshots are scheduled. To do this, enter the following command:

snap sched volume_name 0 0 0