NetApp Snapshot and Cluster-Mode

NetApp Snapshot technology is famous for its uniqueness and ease of use. For example, unlike most competing snapshot technologies, you can create a volume snapshot in seconds, regardless of the size of the volume. It is very efficient in storage space usage.  And you can create hundreds of snapshot copies based on your needs. These excellent features are there for you in Data ONTAP 8.1 operating in cluster-mode.

The familiar 7-mode commands, such as snap reserve, snap sched and snap list, are still operational in cluster-mode. But cluster-mode has a new set of commands (see Fig. 1); which you can explore by simply typing the command (e.g., snap create) and hit return (see Fig. 2).

Figure 1: Cluster-mode snapshot commands

Figure 2: Cluster-mode snap create's usage

One thing I did observe is that the cluster-mode snapshot policy seems to take precedence over the 7-mode snap sched command. The default snapshot policy in cluster-mode is that the hourly, daily and weekly snapshot schedules are enabled, with the following frequency:

  • Hourly: 6
  • Daily: 2
  • Weekly: 2

If you try to set snapshot schedule using the command snap sched <volume name> 0 0 0, meaning don’t take any scheduled snapshot, you will be surprised that this command is ignored; and hourly, daily and weekly snapshot copies are taken.

There are several ways to change the default snapshot policy in cluster-mode. Here are some examples:

     a)     Use the snap policy modify command to disable the policy

     b)     Under the  scope of snapshot policy, use add-schedule, modify-schedule, or remove-schedule to change it to your liking (see Fig. 3)

     c)      You can also use snap policy create to create new snapshot policy

Figure 3: Cluster-mode snapshot policy commands

In summary, the 7-mode commands, by and large, are still valid for snapshot management. But be aware of the new cluster-mode snapshot policy which may take precedence.

Thanks for reading.

Comments
VMUNOZ_NTT

Could you explain the main motives why NetApp change the policy about snapshots?

On ONTAP 8.1 7-Mode (suppose also on cluster mode)  aggr snap reserve default is set at 0% (previously 5%).

However snap sched -A has the same default like previous releases(aggr0: 0 1 4@9,14,19). But this fact results no snaps are created for Aggregates.

Really I didn't need an aggr snap in any case since I know ONTAP, and I read that the protection against WAFL corruption is only useful with syncmirror and metro cluster configurations. Recommends NetApp not to use aggr snaps if syncmirror and/or metro-cluster features are not used? Really the new 8.1 documentation (Release notes, ONTAP guides, etc..) don't clarify how to act...

On the other hand, I found really useful to decrease the default flexvol snap reserve from 20% to 5% to achieve storage efficiency as higher possible.

lwei Former NetApp Employee

VMUNOZ.NTT: good questions. However, I'm afraid I don't have good answers to your questions, except to say that it looked to me those are new code. So, I wouldn't expect them to behave the same. On the other hand, I believe "sched -A" is the existing code that's part of ONTAP 7 and older. I'd say that if you didn't really need agar snap, maybe, stay away from it.

Thanks,

Wei