Release Notes

Linux setup and configuration
24 Dell EMC PowerVault ME4 Series and Linux | 3924-BP-L
Note the following in the prior example:
• The device section identifies the ME4 Series system by its vendor and product tags.
• It is recommended to enable user_friendly_names.
• It is recommended to enable Asymmetric Logical Unit Access (ALUA). See section 3.2.3.
• The path_selector can either be service-time or round-robin.
• When many volumes are mapped on a host, it might be beneficial to create device aliases to make it
easier to find and organize volumes on the host. Use the volume WWN to create multipath device
aliases. See the multipaths section in the prior example. The ME4 Series volume with the WWN of
3600c0ff0003c589f1e4b6b5b01000000 has a multipath device named /dev/mapper/app-data-01 to
reflect the purpose of the volume, instead of the generic name /dev/mapper/mpathb.
3.2.3 Asymmetric Logic Unit Access
ME4 Series storage uses Unified LUN Presentation (ULP), which can expose all LUNs through all host ports
on both controllers. The storage system appears as an active-active system to the host. The host can choose
any available path to access a LUN regardless of disk group ownership. When ULP is in use, the controllers'
operating/redundancy mode is shown as active-active ULP. ULP uses the Asymmetric Logic Unit Access
(ALUA) extensions to negotiate paths with the ALUA-aware hosts. If the host is not ALUA-aware, all paths are
treated as equal by the host even though some paths might have lower latency than others.
To make the Linux host ALUA-aware, set the path_grouping_policy, hardware_handler, and prio
parameters accordingly in the /etc/multipath.conf file. The prior example in section 3.2.2 shows the proper
settings to enable ALUA awareness for ME4 Series storage.
Note: Dell EMC recommends enabling ALUA awareness in Linux multipath to optimize the I/O paths.
After modifying the multipath.conf file, reload the configuration.
# multipath –r
When the ALUA setting is enabled, the path information should look similar to the following example. Two
path groups are formed. Each group consists of one or more paths. The optimized path group has a higher
priority, 50 in the following example, than the non-optimized path group which has a lower priority of 10. The
optimized path group also has active status while the status of the non-optimized path group is enabled.
# multipath -ll mpathb
mpathb (3600c0ff0003c589f1e4b6b5b01000000) dm-6 DellEMC ,ME4
size=200G features='0' hwhandler='1 alua' wp=rw
|-+- policy='service-time 0' prio=50 status=active
| |- 18:0:5:0 sdd 8:48 active ready running
| `- 19:0:5:0 sdj 8:144 active ready running
`-+- policy='service-time 0' prio=10 status=enabled
|- 18:0:4:0 sdl 8:176 active ready running
`- 19:0:4:0 sdi 8:128 active ready running
3.3 LUN partition
In general, partitions (and partition tables) are not required for volumes other than the boot volume or for
applications with very specific requirements. Dell EMC recommends using the whole volume instead of