Pool creation errors can occur for many reasons. Some reasons are obvious, such as when a specified device doesn't exist, while other reasons are more subtle.
Before formatting a device, ZFS first determines if the disk is in-use by ZFS or some other part of the operating system. If the disk is in use, you might see errors such as the following:
# zpool create tank c1t0d0 c1t1d0 invalid vdev specification use '-f' to override the following errors: /dev/dsk/c1t0d0s0 is currently mounted on /. Please see umount(1M). /dev/dsk/c1t0d0s1 is currently mounted on swap. Please see swap(1M). /dev/dsk/c1t1d0s0 is part of active ZFS pool zeepool. Please see zpool(1M).
The disk or one of its slices contains a file system that is currently mounted. To correct this error, use the umount command.
The disk contains a file system that is listed in the /etc/vfstab file, but the file system is not currently mounted. To correct this error, remove or comment out the line in the /etc/vfstab file.
The disk is in use as the dedicated dump device for the system. To correct this error, use the dumpadm command.
The disk or file is part of an active ZFS storage pool. To correct this error, use the zpool destroy command to destroy the other pool, if it is no longer needed. Or, use the zpool detach command to detach the disk from the other pool. You can only detach a disk from a mirrored storage pool.
The following in-use checks serve as helpful warnings and can be overridden by using the –f option to create the pool:
The disk contains a known file system, though it is not mounted and doesn't appear to be in use.
The disk is part of a Solaris Volume Manager volume.
The disk is part of a storage pool that has been exported or manually removed from a system. In the latter case, the pool is reported as potentially active, as the disk might or might not be a network-attached drive in use by another system. Be cautious when overriding a potentially active pool.
The following example demonstrates how the –f option is used:
# zpool create tank c1t0d0 invalid vdev specification use '-f' to override the following errors: /dev/dsk/c1t0d0s0 contains a ufs filesystem. # zpool create -f tank c1t0d0
Ideally, correct the errors rather than use the –f option to override them.
Creating pools with virtual devices of different replication levels is not recommended. The zpool command tries to prevent you from accidentally creating a pool with mismatched levels of redundancy. If you try to create a pool with such a configuration, you see errors similar to the following:
# zpool create tank c1t0d0 mirror c2t0d0 c3t0d0 invalid vdev specification use '-f' to override the following errors: mismatched replication level: both disk and mirror vdevs are present # zpool create tank mirror c1t0d0 c2t0d0 mirror c3t0d0 c4t0d0 c5t0d0 invalid vdev specification use '-f' to override the following errors: mismatched replication level: 2-way mirror and 3-way mirror vdevs are present
You can override these errors with the –f option, but you should avoid this practice. The command also warns you about creating a mirrored or RAID-Z pool using devices of different sizes. Although this configuration is allowed, mismatched levels of redundancy result in unused disk space on the larger device. The –f option is required to override the warning.
Attempts to create a pool can fail unexpectedly in different ways, and formatting disks is a potentially harmful action. For these reasons, the zpool create command has an additional option, –n, which simulates creating the pool without actually writing to the device. This dry run option performs the device in-use checking and replication-level validation, and reports any errors in the process. If no errors are found, you see output similar to the following:
# zpool create -n tank mirror c1t0d0 c1t1d0 would create 'tank' with the following layout: tank mirror c1t0d0 c1t1d0
Some errors cannot be detected without actually creating the pool. The most common example is specifying the same device twice in the same configuration. This error cannot be reliably detected without actually writing the data, so the zpool create –n command can report success and yet fail to create the pool when the command is run without this option.
When a pool is created, the default mount point for the top-level file system is /pool-name. This directory must either not exist or be empty. If the directory does not exist, it is automatically created. If the directory is empty, the root file system is mounted on top of the existing directory. To create a pool with a different default mount point, use the –m option of the zpool create command. For example:
# zpool create home c1t0d0 default mountpoint '/home' exists and is not empty use '-m' option to provide a different default # zpool create -m /export/zfs home c1t0d0
This command creates the new pool home and the home file system with a mount point of /export/zfs.
For more information about mount points, see Managing ZFS Mount Points.