Messing with disk exchange and no errors

[Sir.Robin]

So i wanted to change all drives in my 6 drive raidz2 array on NAS02, and proceed to exchange them one by one, resilvering every exchange.

CIFS were disabled during the process.

I did hotswap during these exchanges and i do have backup, so no worries.

However, the last drive beeing exchanged (da5), i accidentily disconnected BEFORE the resilver on the previous exchange (da4) reached 100%. Now, resilvering started over again on both drives.

After thinking about it, i shut down my server before ANY of the resilvering processes finished. Reconnected the da5 drive that was disconnected too early (the old one), and booted the server.

zpool status then shows resilvering process started again on da4, but another drive (da2) is offline. I somehow disconnected power to it while reconnecting da5.

I shut down again. Before resilver finished on da4. reconnect power to da2 and boot the server. All drives is now online and resilver on da4 is yet again running.

Now i wait for resilver to finish on da4 and it does. Without any fuzz.

Then proceed to exchange the da5 again and resilver the new da5. No problem. all drives are at this point exchanged.

Now, lastly, i do a scrub on this pool... and despite all the mess i made, it finishes successfully and no errors repaired..!!?

How is it possible that no errors occured to this pool after all this mess??

 

[Ericloewe]

RAIDZ2, right? So, assuming you replaced drives without the new one resilvering with the pool still intact, you'd still end up with a viable pool, just one that can be brought down by a single failure. Besides, if you reattach a drive that was part of the pool, ZFS will just resilver any small bits that have changed.

 

[Sir.Robin]

It seems pretty recilliant yes :) I was just a bit surprised since i did two shut downs in the middle of resilvering and also disconnected and reconnected different drives. Good to know.

 

[Robert Trevellyan]

I was just a bit surprised since i did two shut downs in the middle of resilvering and also disconnected and reconnected different drives

Congratulate yourself for choosing RAIDZ2 for your vdev layout. Your scenario would have ended differently with RAIDZ1.

 

[Sir.Robin]

Congratulate yourself for choosing RAIDZ2 for your vdev layout. Your scenario would have ended differently with RAIDZ1.

Yes probably.
I did once... couple of years back... while replacing a faulted drive, i reconnected the new one hot. The other two drives on the same power lane reset. Causing the pool to go offline and FreeNAS locked up.
After a reboot, all was ok again and i could resilver the replaced drive. :)