Home > Storage > PowerVault > Guides > Dell PowerVault ME5 Series and Linux > Discover and identify ME5 volumes
After creating and enabling host access of the LUNs in the ME5 storage system, the Linux host needs to scan for these new LUNs before they can be used. The following software packages contain useful utilities to discover and identify LUNs.
After attaching the volumes to a Linux host, identify the volumes by either LUN IDs or WWNs. First, gather the volume information on the ME5 storage system in PowerVault Manager.
Both LUN IDs and WWNs can also be displayed using the ME5 CLI command. The following example shows the mapped volumes to a host. The returned information contains the LUN IDs and Serial Numbers (WWNs).
# ssh manage@{controller-IP-address}
# show maps all {host}.*
# show maps all glx4.*
Host View [Serial Number (00c0ff64634c000051c2776301010000) Host Name (glx4.*) ] Mapping:
Volume Serial Number LUN Access Ports
-----------------------------------------------------------------------
testvol1 00c0ff64634c0000ae88726301000000 0 read-write 0,1,2,3
testvol2 00c0ff64639b0000af88726301000000 1 read-write 0,1,2,3
New volumes are added to the Linux host by scanning the SCSI buses that have access to the ME5 Series system. The sg3_utils package provides the rescan-scsi-bus.sh script that helps simplify the process.
By default, LUN ID 0 is assigned to the ME5 Series storage system on the Linux host. This assignment is completed when the host has visibility to the ME5 Series system, for example, when FC zones are created for the host and ME5 Series system, or when the host iSCSI initiator logs in to ME5 Series iSCSI ports. The lsscsi command shows that the ME5 storage system enclosure has been assigned ID 0 on a Linux host.
# lsscsi -is|grep ME5
[11:0:10:0] enclosu DellEMC ME5 I200 - - -
[11:0:11:0] enclosu DellEMC ME5 I200 - - -
[11:0:12:0] enclosu DellEMC ME5 I200 - - -
[11:0:13:0] enclosu DellEMC ME5 I200 - - -
[12:0:10:0] enclosu DellEMC ME5 I200 - - -
[12:0:11:0] enclosu DellEMC ME5 I200 - - -
[12:0:12:0] enclosu DellEMC ME5 I200 - - -
[12:0:13:0] enclosu DellEMC ME5 I200 - - -
When attaching the ME5 volumes to a Linux host, the ME5 storage system automatically assigns LUN IDs starting at 0. This creates a conflict on the Linux host where LUN ID 0 has already been assigned to the ME5 storage system enclosure.
To reclaim the ID 0 on the Linux host for the volume, run the rescan-scsi-bus.sh script with the --forcerescan option.
# rescan-scsi-bus.sh --forcerescan
After the volume is successfully mapped to LUN ID 0 on the Linux host, the subsequent scanning can be done without the --forcerescan option.
# /usr/bin/rescan-scsi-bus.sh -a
The lsscsi command shows the ID 0 has been reclaimed for the ME5 volume.
# lsscsi -is|grep ME5
[11:0:10:0] disk DellEMC ME5 I200 /dev/sdb 3600c0ff00064634cae88726301000000 199GB
[11:0:11:0] disk DellEMC ME5 I200 /dev/sdc 3600c0ff00064634cae88726301000000 199GB
[11:0:12:0] disk DellEMC ME5 I200 /dev/sdd 3600c0ff00064634cae88726301000000 199GB
[11:0:13:0] disk DellEMC ME5 I200 /dev/sde 3600c0ff00064634cae88726301000000 199GB
[12:0:10:0] disk DellEMC ME5 I200 /dev/sdf 3600c0ff00064634cae88726301000000 199GB
[12:0:11:0] disk DellEMC ME5 I200 /dev/sdg 3600c0ff00064634cae88726301000000 199GB
[12:0:12:0] disk DellEMC ME5 I200 /dev/sdh 3600c0ff00064634cae88726301000000 199GB
[12:0:13:0] disk DellEMC ME5 I200 /dev/sdi 3600c0ff00064634cae88726301000000 199GB
Note: Only use the --forcerescan option for removing the enclosure entry and reclaiming LUN 0.
The ME5 Series storage system automatically assigns a unique LUN ID when the volume is attached to a host. The Attach Volume operation does not allow specifying a LUN ID directly. After attaching the volume to a host, the LUN ID can be changed if necessary, using the following procedure.
# scan-bus-rescan.sh -a
Note: The volume must first be attached to a host before the LUN ID can be changed.
On the Linux host, run the lsscsi command to show the volume LUN IDs and WWNs. The highlighted digits in red correspond to the LUN IDs; the highlights in blue correspond to the WWNs.
# lsscsi -is|grep ME5
[11:0:10:0] disk DellEMC ME5 I200 /dev/sdj 3600c0ff00064634cae88726301000000 249GB
[11:0:10:1] disk DellEMC ME5 I200 /dev/sdb 3600c0ff00064639baf88726301000000 349GB
… Truncated for brevity
Using WWNs to identify the volumes is more precise because WWNs are unique on the storage system and on the host, and they are immutable. This method reduces the chance of confusion if the LUN IDs are changed unintentionally.
It is common to set up persistent device mapping to set custom device file names, file ownership, and permission. This can be achieved by creating udev rules that search for specific WWNs, rename device files, and make ownership and permission changes.
If DM-multipath is enabled, the multipath command also shows the WWNs for the multipath devices. The individual paths of the multipath devices include the LUN IDs.
These options are detailed as follows:
# multipath -l mpathb
mpathb (3600c0ff00064639baf88726301000000) dm-4 DellEMC,ME5
size=326G features='0' hwhandler='1 alua' wp=rw
|-+- policy='service-time 0' prio=0 status=active
| |- 11:0:12:1 sdd 8:48 active undef running
| |- 11:0:13:1 sde 8:64 active undef running
| |- 12:0:12:1 sdh 8:112 active undef running
| `- 12:0:13:1 sdi 8:128 active undef running
`-+- policy='service-time 0' prio=0 status=enabled
|- 11:0:10:1 sdb 8:16 active undef running
|- 11:0:11:1 sdc 8:32 active undef running
|- 12:0:10:1 sdf 8:80 active undef running
`- 12:0:11:1 sdg 8:96 active undef running
# ls -1 /dev/sd[a-z] /dev/dm*|while read path
do
(echo $path:; /usr/lib/udev/scsi_id --page=0x83 --whitelisted --device=$path)|xargs -n 2
done
/dev/dm-0: 361866da0b2044b00242c056d06e494f7
/dev/dm-1: 361866da0b2044b00242c056d06e494f7
/dev/dm-2: 361866da0b2044b00242c056d06e494f7
/dev/dm-3: 3600c0ff00064634cae88726301000000
/dev/dm-4: 3600c0ff00064639baf88726301000000
/dev/sda: 361866da0b2044b00242c056d06e494f7
/dev/sdb: 3600c0ff00064639baf88726301000000
/dev/sdc: 3600c0ff00064639baf88726301000000
/dev/sdd: 3600c0ff00064639baf88726301000000
/dev/sde: 3600c0ff00064639baf88726301000000
/dev/sdf: 3600c0ff00064639baf88726301000000
/dev/sdg: 3600c0ff00064639baf88726301000000
/dev/sdh: 3600c0ff00064639baf88726301000000
/dev/sdi: 3600c0ff00064639baf88726301000000
/dev/sdj: 3600c0ff00064634cae88726301000000
/dev/sdk: 3600c0ff00064634cae88726301000000
/dev/sdl: 3600c0ff00064634cae88726301000000
/dev/sdm: 3600c0ff00064634cae88726301000000
/dev/sdn: 3600c0ff00064634cae88726301000000
/dev/sdo: 3600c0ff00064634cae88726301000000
/dev/sdp: 3600c0ff00064634cae88726301000000
/dev/sdq: 3600c0ff00064634cae88726301000000
When ME5 volumes are attached to a Linux operating system in a VMware virtual machine as in-guest iSCSI volumes, the operating system might not detect the ME5 volume WWNs. To allow the virtual machine to present the iSCSI volume WWNs, make sure that the disk.EnableUUID configuration parameter is set to True on the virtual machine.
In vSphere client, edit the virtual machine settings. Click Settings > VM Options > Advanced > Configuration Parameters. Click ADD CONFIGURATION PARAMS. Enter or update the following configuration parameter:
Parameter name: disk.EnableUUID
Parameter value: TRUE