Dell EMC Metro node 7.1 Administrator Guide

Performing thin mirroring

If you attach a mirror to a thin-capable device and that mirror is not thin, the resulting RAID 1 device loses its thin-capability.

When you run the device attach-mirror -d command to attach a thick mirror leg to a thin-capable device, a warning stating that the device is not thin-capable is displayed. You are also prompted to confirm that you want to continue. You can use the --force option to bypass the confirmation, but the resulting device is not thin.

VPlexcli:/clusters/cluster-1/storage-elements/extents> device attach-mirror -d myDevice
-m extent_TOP_101_1

The top-level device 'myDevice' is thin-capable. After attaching the mirror, the new
top-level device will not be thin-capable.  Do you wish to proceed? (Yes/No) no

device attach-mirror:  Evaluation of <<device attach-mirror -d myDevice -m extent_TOP_101_1>> failed.
cause:                 Failed to attach mirror.
cause:                 Operation was halted by the user
VPlexcli:/clusters/cluster-1/storage-elements/extents>

You can attach a mirror to a device already supporting a thin-enabled virtual-volume using the device attach-mirror command.

To add a thick mirror leg to a thin-enabled virtual-volume, you can continue by:

• Setting the virtual-volume's thin-enabled property to false using the set command. The new virtual-volume is not thin-enabled, nor thin-capable.

  VPlexcli:/clusters/cluster-1/devices> set ../virtual-volumes/myVolume::thin-enabled false
  VPlexcli:/clusters/cluster-1/devices> device attach-mirror --device myDevice --mirror myMirror
  VPlexcli:/clusters/cluster-1/devices>
  

• Using the --force option with the device attach-mirror command. The new virtual-volume is not thin-enabled, nor thin-capable.

  VPlexcli:/clusters/cluster-1/devices> device attach-mirror --device myDevice --mirror myMirror
  VPlexcli:/clusters/cluster-1/devices>
  

In a mirrored thin setup, all the legs must come from the same storage-array family. If you try to create thin legs from the arrays that belong to different storage-array family, the thin personality of the legs are lost and they stop supporting the thin storage management features. The following is an example for such a scenario:

VPlexcli:/> device attach-mirror --device xio_device --mirror vnx_device
Thin-capability is only supported with homogeneous storage-array types. The top-level device
'xio_device' is supported by XtremIO but the mirror 'vnx_device' is supported by CLARiiON.
Since XtremIO and CLARiiON are not homogeneous, the top-level device will lose thin-capability
after the new mirror is attached. Do you wish to proceed?  (Yes/No) No

device attach-mirror:  Evaluation of <<device attach-mirror --device xio_device --mirror vnx_device>>
                       failed.
cause:                 Unable to attach mirror 'vnx_device' to device 'xio_device'.
cause:                 Operation was halted by the user

VPlexcli:/>