Scrubbing took 0h0m?

[TonyToews]

So as recommended I run the scrub on my new FreeNAS system from the GUI. After a minute or two I go to the shell and run "zpool status" And it states that scrubbing took 0h0m. Now I'm real dumb when it comes to *nix but even I know that's kinda fast. :)

Any ideas?

 

[peterh]

It's normal.
scrub will compare USED DATA ( as will zfs) , an empty filesystem will be scrubed fast !

And yes *nix is normally fast and efficient an most respects !

 

[TonyToews]

Ohhhh. I assumed that it would do the entire hard drive. Not just the data portion. Does it read every sector of every file then? Or to ask another question. What does scrubbing actually do? There's no description in the docs.

 

[peterh]

zfs creates disk volumes from a pool of storage. The pool is just a bunch of blocks. A volume is a named collection of blocks that has properties ( mirrored raid 5 for exampel). But it's only used blocks that is referenced ( the empty
ones will be allocated when needed).
Scrub is a process where valitity of data is done ( checksum ok, mirror/raid5 ok etc) , it's simular to rebuilding
when a drive is replaced, then the same process is done but this time the result is used to rebuild a drive.

 

[TonyToews]

Peter, yes, that makes sense. I was thinking pretty much the same, although not that detailed of course, after I left the computer for the evening but I didn't feel like coming back to type my thoughts in.

To me the key thing is that to check the file structure it also has to read every allocated byte. Which is a good exercise to see if the hard drive is going to fail too.

Also on a few hundred Gb used so far it took 0h8m so that's reasonable. And I see I have several status emails from FreeNAS.

 

[peterh]

To check the actual disks you can enable smartd and configure tests for it.

 

[TonyToews]

Yes, I have enabled smartd and set the alert temps to 10 C so I got warning emails. Then set them to 40 C as that was just a bit higher than the temps reported.

After throwing on several TB of files scrubbing took 5 hours which seems quite reasonable to me. I have several more days of file transfer at 100 mpbs from my other systems before I'm done.