Hardware Installation and Maintenance Guide, Version 11.60.2 - Accessing NVMe volumes for virtual device targets (DM-MP devices)

For SLES 12, I/O is directed to virtual device targets by the Linux host. DM-MP manages the physical paths underlying these virtual targets.

Virtual devices are I/O targets

Make sure you are running I/O only to the virtual devices created by DM-MP and not to the physical device paths. If you are running I/O to the physical paths, DM-MP cannot manage a failover event and the I/O fails.

You can access these block devices through the dm device or the symlink in /dev/mapper, for example:

/dev/dm-1
/dev/mapper/eui.00001bc7593b7f5f00a0980000af4462

Example

The following example output from the nvme list command shows the host node name and its correlation with the namespace ID.


NODE         SN           MODEL           NAMESPACE

/dev/nvme1n1 021648023072 NetApp E-Series 10
/dev/nvme1n2 021648023072 NetApp E-Series 11
/dev/nvme1n3 021648023072 NetApp E-Series 12
/dev/nvme1n4 021648023072 NetApp E-Series 13
/dev/nvme2n1 021648023151 NetApp E-Series 10
/dev/nvme2n2 021648023151 NetApp E-Series 11
/dev/nvme2n3 021648023151 NetApp E-Series 12
/dev/nvme2n4 021648023151 NetApp E-Series 13

Column Description

Column	Description
`Node`	The node name includes two parts: The notation `nvme1` represents controller A and `nvme2` represents controller B. The notation `n1`, `n2`, and so on represent the namespace identifier from the host perspective. These identifiers are repeated in the table, once for controller A and once for controller B.
`Namespace`	The Namespace column lists the namespace ID (NSID), which is the identifier from the storage array perspective.

Node

The node name includes two parts:

The notation nvme1 represents controller A and nvme2 represents controller B.
The notation n1, n2, and so on represent the namespace identifier from the host perspective. These identifiers are repeated in the table, once for controller A and once for controller B.

Namespace

The Namespace column lists the namespace ID (NSID), which is the identifier from the storage array perspective.

In the following multipath -ll output, the optimized paths are shown with a prio value of 50, while the non-optimized paths are shown with a prio value of 10.

The Linux operating system routes I/O to the path group that is shown as status=active, while the path groups listed as status=enabled are available for failover.

eui.00001bc7593b7f500a0980000af4462 dm-0 NVME,NetApp E-Series
size=15G features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=50 status=active
| `- #:#:#:# nvme1n1 259:5 active ready running
`-+- policy='service-time 0' prio=10 status=enabled
  `- #:#:#:# nvme2n1 259:9  active ready running

eui.00001bc7593b7f5f00a0980000af4462 dm-0 NVME,NetApp E-Series
size=15G features='1 queue_if_no_path' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=0 status=enabled
| `- #:#:#:# nvme1n1 259:5 failed faulty running
`-+- policy='service-time 0' prio=10 status=active
  `- #:#:#:# nvme2n1 259:9  active ready running

Line item	Description
`policy='service-time 0' prio=50 status=active`	This line and the following line show that `nvme1n1`, which is the namespace with an NSID of 10, is optimized on the path with a `prio` value of 50 and a `status` value of `active`. This namespace is owned by controller A.
`policy='service-time 0' prio=10 status=enabled`	This line shows the failover path for namespace 10, with a `prio` value of 10 and a `status` value of `enabled`. I/O is not being directed to the namespace on this path at the moment. This namespace is owned by controller B.
`policy='service-time 0' prio=0 status=enabled`	This example shows `multipath -ll` output from a different point in time, while controller A is rebooting. The path to namespace 10 is shown as `failed faulty running` with a `prio` value of 0 and a `status` value of `enabled`.
`policy='service-time 0' prio=10 status=active`	Note that the `active` path refers to `nvme2`, so the I/O is being directed on this path to controller B.