New to NetApp? Here are the default Snapshot settings explained for ONTAP 8.1Posted: June 18, 2013
Snapshots are enabled by default when a volume is created. They follow the schedule as seen from the CLI command snap sched: 0 2 6@8,12,16,20
and from the System Manager GUI. Note the default Snapshot Reserve is 5% and that the checkbox for Enable scheduled Snapshots is checked by default.
The snap sched command shows zero weekly snapshots are taken (and therefore zero are kept at any one time), two daily snapshots are kept, and six hourly snapshots are kept. The hourly snapshots are, by default, taken at 8am, 12 noon, 4pm, and 8pm. Hence the output of the snap sched command: 0 2 6@8,12,16,20
So if you left your new volume to run on its own for at least a couple days, you’d see snapshots listed using snap list as such:
Count the hourly snapshots: there are 6, numbered from hourly.0 to hourly.5, with hourly.0 being the latest. Looking at the times these snaps were taken, you can see they correspond to the default times, 8am, 12 noon, 4pm, and 8pm.
Count the daily snapshots: there are 2, nighly.0 and nightly.1, with nightly.0 being the latest. Looking at the time these snaps were taken, you can see that, by default, daily snaps are taken at midnight.
Finally, count the weekly snapshots: there are none. This is because, by default, no weekly snapshots are taken. When weekly snapshots *are* taken, however, they’re taken at midnight on Sundays and show up as weekly.N. For example, weekly.0, weekly.1, and so on.
Take note of the %/used and %total columns, as this is critical to ensuring that when using the default volume settings, your volumes don’t go offline. If your change rates and snapshot schedules are such that you’re going to fill up the volume before snapshots are automatically deleted and a LUN is thin provisioned, then your LUN will go offline. So knowing change rates is very useful, as you already know. I imagine NetApp chose the default snapshot schedule to meet most needs, but still, sizing volumes, reserves, and setting LUN protection options like autogrow and autodelete are still very important.