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SAN hosts and cloud clients

Use Ubuntu 20.04 with ONTAP

Contributors netapp-ranuk

You can use the ONTAP SAN host configuration settings to configure Ubuntu 20.04 with ONTAP as the target.

Note NetApp Linux Unified Host Utilities software package is not available for Ubuntu 20.04 OS.

SAN booting

What you'll need

If you decide to use SAN booting, it must be supported by your configuration. You can use the NetApp Interoperability Matrix Tool to verify that your OS, HBA, HBA firmware and the HBA boot BIOS, and ONTAP version are supported.

Steps

  1. Map the SAN boot LUN to the host.

  2. Verify that multiple paths are available.

    Note Multiple paths become available after the host OS is up and running on the paths.

  3. Enable SAN booting in the server BIOS for the ports to which the SAN boot LUN is mapped.

    For information on how to enable the HBA BIOS, see your vendor-specific documentation.

  4. Reboot the host to verify that the boot is successful.

Multipathing

For Ubuntu 20.04, the /etc/multipath.conf file must exist, but you do not need to make specific changes to the file. Ubuntu 20.04 is compiled with all the settings required to recognize and correctly manage ONTAP LUNs.

You can use the multipath -ll command to verify the settings for your ONTAP LUNs.
The following sections provide sample multipath output for a LUN mapped to ASA and non-ASA personas.

All SAN Array configurations

In All SAN Array (ASA) configurations, all paths to a given LUN are active and optimized. This improves performance by serving I/O operations through all paths at the same time.

Example

The following example displays the correct output for an ONTAP LUN:

# multipath -ll
3600a098038314559533f524d6c652f62 dm-24 NETAPP,LUN C-Mode
size=10G features='3 queue_if_no_path pg_init_retries 50' hwhandler='1 alua' wp=rw
`-+- policy='service-time 0' prio=50 status=active
  |- 11:0:1:13 sdm  8:192  active ready running
  |- 11:0:3:13 sdah 66:16  active ready running
  |- 12:0:1:13 sdbc 67:96  active ready running
  `- 12:0:3:13 sdbx 68:176 active ready running
Note Do not use an excessive number of paths to a single LUN. No more than four paths should be required. More than eight paths might cause path issues during storage failures.

Non-ASA configurations

For non-ASA configurations, there should be two groups of paths with different priorities. The paths with the higher priorities are Active/Optimized, meaning they are serviced by the controller where the aggregate is located. The paths with the lower priorities are active but are non-optimized because they are served from a different controller. The non-optimized paths are only used when no optimized paths are available.

Example

The following example displays the correct output for an ONTAP LUN with two Active/Optimized paths and two Active/Non-Optimized paths:

# multipath -ll
3600a098038314837352453694b542f4a dm-0 NETAPP,LUN C-Mode
size=160G features='3 queue_if_no_path pg_init_retries 50' hwhandler='1 alua' wp=rw
|-+- policy='service-time 0' prio=50 status=active
| |- 14:0:3:0 sdbk 67:224 active ready running
| `- 15:0:2:0 sdbl 67:240 active ready running
`-+- policy='service-time 0' prio=10 status=enabled
  |- 14:0:0:0 sda  8:0    active ready running
  `- 15:0:1:0 sdv  65:80  active ready running
Note Do not use an excessive number of paths to a single LUN. No more than four paths should be required. More than eight paths might cause path issues during storage failures.

The Ubuntu 20.04 OS is compiled to recognize ONTAP LUNs and automatically set all configuration parameters correctly for both ASA and non-ASA configurations. You can further optimize performance for your host configuration with the following recommended settings.

The multipath.conf file must exist for the multipath daemon to start, but you can create an empty, zero-byte file by using the following command:

touch /etc/multipath.conf

The first time you create this file, you might need to enable and start the multipath services:

# systemctl enable multipathd
# systemctl start multipathd

  • There is no requirement to add anything directly to the multipath.conf file, unless you have devices that you do not want to be managed by multipath or you have existing settings that override defaults.

  • To exclude unwanted devices, add the following syntax to the multipath.conf file .

    blacklist {
        wwid <DevId>
        devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
        devnode "^hd[a-z]"
        devnode "^cciss.*"
}

    Replace the <DevId> with the WWID string of the device you want to exclude.

    Example

    In this example, we are going to determine the WWID of a device and add to the multipath.conf file.

    Steps

    1. Run the following command to determine the WWID:

      # /lib/udev/scsi_id -gud /dev/sda
360030057024d0730239134810c0cb833

      sda is the local SCSI disk that we need to add it to the blacklist.

    2. Add the WWID to the blacklist stanza in /etc/multipath.conf:

      blacklist {
     wwid   360030057024d0730239134810c0cb833
     devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
     devnode "^hd[a-z]"
     devnode "^cciss.*"
}

You should always check your /etc/multipath.conf file for legacy settings, especially in the defaults section, that might be overriding the default settings.

The following table demonstrates the critical multipathd parameters for ONTAP LUNs and the required values. If a host is connected to LUNs from other vendors and any of these parameters are overridden, they will need to be corrected by later stanzas in the multipath.conf file that apply specifically to ONTAP LUNs. If this is not done, the ONTAP LUNs might not work as expected. These defaults should only be overridden in consultation with NetApp and/or an OS vendor and only when the impact is fully understood.

Parameter Setting

detect_prio

yes

dev_loss_tmo

"infinity"

failback

immediate

fast_io_fail_tmo

5

features

"2 pg_init_retries 50"

flush_on_last_del

"yes"

hardware_handler

"0"

no_path_retry

queue

path_checker

"tur"

path_grouping_policy

"group_by_prio"

path_selector

"service-time 0"

polling_interval

5

prio

"ontap"

product

LUN.*

retain_attached_hw_handler

yes

rr_weight

"uniform"

user_friendly_names

no

vendor

NETAPP
Example

The following example shows how to correct an overridden default. In this case, the multipath.conf file defines values for path_checker and no_path_retry that are not compatible with ONTAP LUNs. If they cannot be removed because other SAN arrays are still attached to the host, these parameters can be corrected specifically for ONTAP LUNs with a device stanza.

defaults {
   path_checker      readsector0
   no_path_retry     fail
}

devices {
   device {
      vendor         "NETAPP  "
      product         "LUN.*"
      no_path_retry    queue
      path_checker     tur
   }
}

KVM settings

You can use the recommended settings to configure Kernel-based Virtual Machine (KVM) as well. There are no changes required to configure KVM as the LUN is mapped to the hypervisor.

Known issues

There are no known issues for the Ubuntu 20.04 with ONTAP release.