Add a function to return last scrub date for a pool.

[SimonGreenaway]

Describe the feature you would like to see added to OpenZFS

Add 'zpool get lastscrub mypool' to return the last scrub timestamp in a suitable format.

This will allow incremental scrubs for versions >=2.4.0 by retrieving the last scrub date and starting an incremental scrub. It should also be possible to add a 'zpool autoscrub mypool' that scrubs from the last scrub date to the current time.

How will this feature improve OpenZFS?

Incremental scrubs will improving scrub times on large or slow datasets, this feature request would make it easier to use.

Additional context

[mabod]

What is an "incremental scrub" for you? Do you mean "scrub only data that is new"? Or do you mean "do only scrub data that was not scrubbed last time"?

[SimonGreenaway]

My use case is to scrub new data since the last scrub. Of course, if a -E option is used on the last scrub it would be meaningless but I suspect most people will use -S and not the -E.

I could currently pass the results of zpool status to find the last scrub time, but thought a zpool get option would be a cleaner way of doing it.

[mabod]

I could currently pass the results of zpool status to find the last scrub time

or you could use the pools history: zpool history poolname | grep scrub | tail -n 1