ZFS on Linux: Which mountpoint option when mounting manually per script?

MelBourbon asked:

I want to create a zpool with ZFS on Linux (7.13) on Ubuntu 18.04. The problem is that the pool will be created based on LUKS encrypted drives (not root, only external). These drives are decrypted and loaded during boot by a script which i created since they are pulling a key file from an external source.

To avoid any issues with timing where the system wants to mount the zpool before the drives are decrypted and loaded I would like to mount the pool also manually as part of the script.

Now I ask myself which option I should choose for the mountpoint at creating the pool: none or legacy

The man page does not really help what the real difference is:

If a file system’s mount point is set to legacy ZFS makes no attempt to manage the file system, and the administrator is responsible for mounting and unmounting the file system. Because pools must be imported before a legacy mount can succeed, administrators should ensure that legacy mounts are only attempted after the zpool import process finishes at boot time. For example, on machines using systemd, the mount option

Does anybody know the real differences and how to achieve a manual mounting later by script the best way?

My answer:


I’ve been using ZFS pools on LUKS encrypted volumes for the better part of a decade. It works fine.

There is no reason to mount the pool manually to attempt to defeat nonexistent timing problems. Just create your pool normally and enjoy.

To avoid any problems in the future, when creating and managing the pool, use the names beginning with luks- in the /dev/mapper directory to refer to the devices. For example, the devices:

lrwxrwxrwx. 1 root root 10 Jul 26 22:22 luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WCC1P1046856 -> ../../dm-5
lrwxrwxrwx. 1 root root 10 Jul 26 22:22 luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WCC1P1145175 -> ../../dm-4
lrwxrwxrwx. 1 root root 10 Jul 26 22:22 luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WCC1P1165144 -> ../../dm-2
lrwxrwxrwx. 1 root root 10 Jul 26 22:22 luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WMC1P0DHH53R -> ../../dm-3

correspond to:

  pool: srv
 state: ONLINE
  scan: scrub repaired 0B in 0h42m with 0 errors on Tue Jul 30 14:42:04 2019
config:

        NAME                                                 STATE     READ WRITE CKSUM
        srv                                                  ONLINE       0     0     0
          mirror-0                                           ONLINE       0     0     0
            luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WCC1P1046856  ONLINE       0     0     0
            luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WCC1P1145175  ONLINE       0     0     0
          mirror-1                                           ONLINE       0     0     0
            luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WCC1P1165144  ONLINE       0     0     0
            luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WMC1P0DHH53R  ONLINE       0     0     0

This pool is created with:

zpool create -o ashift=12 srv \
    mirror \
        luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WCC1P1046856 \
        luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WCC1P1145175 \
    mirror \
        luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WCC1P1165144 \
        luks-ata-WDC_WD2000FYYZ-01UL1B1_WD-WMC1P0DHH53R

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