ZFS: Replacing a drive with a larger drive within a vdev

One way to expand the capacity of a zpool is to replace each disk with a larger disk; once the last disk is replaced the pool can be expanded (or will auto-expand, depending on your pool settings). To do this we do the following:  
zpool replace [poolname] [old drive] [new drive]  
e.g.:  
zpool replace kepler ata-WDC_WD15EARX-00PASB0_WD-WCAZAA512624 ata-WDC_WD20EARX-00PASB0_WD-WCAZAA637471
If you then check on the pool’s status via zpool status, we see:  
NAME                                            STATE     READ WRITE CKSUM kepler                                          ONLINE     0     0     0 raidz2-0                                      ONLINE     0     0     0 ata-WDC_WD20EARX-00PASB0_WD-WMAZA7352703    ONLINE       0     0     0 replacing-1                                 ONLINE     0     0     0 ata-WDC_WD15EARX-00PASB0_WD-WCAZAA512624  ONLINE      0     0     0 ata-WDC_WD20EARX-00PASB0_WD-WCAZAA637471  ONLINE       0     0     0  (resilvering)  
The pool will resilver and copy the drive contents across. If you have large drives which are reasonably full this resilver process can take quite a few hours. You can do this with multiple drives at once; here’s a zpool  
        NAME                                            STATE     READ WRITE CKSUM kepler                                          ONLINE     0     0     0 raidz2-0                                      ONLINE     0     0     0 ata-WDC_WD20EARX-00PASB0_WD-WMAZA7352703    ONLINE       0     0     0 replacing-1                                 ONLINE     0     0     0 ata-WDC_WD15EARX-00PASB0_WD-WCAZAA512624  ONLINE      0     0     0 ata-WDC_WD20EARX-00PASB0_WD-WCAZAA637471  ONLINE       0     0     0  (resilvering) replacing-2                                 ONLINE       0     0     0 ata-ST2000DM001-9YN164_W24009TB           ONLINE       0     0     0 ata-WDC_WD20EARS-00MVWB0_WD-WCAZAC389099  ONLINE       0     0     0  (resilvering) ata-WDC_WD20EFRX-68AX9N0_WD-WMC300005367    ONLINE       0     0     0 ata-WDC_WD20EARX-00MMMB0_WD-WCAWZ0842974    ONLINE       0     0     0 ata-WDC_WD20EARX-00PASB0_WD-WMAZA7482198    ONLINE       0     0     0
Please don’t disconnect the old drive before inserting the new one – this can cause issues with some setups where ZFS complains that it cannot find the old drive to replace.   Once your resilver is complete on the final drive you can expand the vdev by running:  
zpool online -e [poolname]  
or you can turn on automatic expansion with the following settings:  
zfs set autoexpand=on [poolname]  
If you are using zpool online -e the pool does not have to be offline for it to work. Now sit back and enjoy your increased space!