[ovirt-users] oVirt 4.0 and multipath.conf for HPE 3PAR. What do you advise?

[aleksey.maksimov at it-kb.ru]

Nir Soffer, thank you very much for your explanation.
Trick with "# VDSM PRIVATE" works great.

14.08.2016, 14:22, "Nir Soffer" <nsoffer at redhat.com>:
> On Sat, Aug 13, 2016 at 4:03 PM, <aleksey.maksimov at it-kb.ru> wrote:
>>  Hello, oVirt guru's !
>>
>>  I installed oVirt 4.0 on several servers HP ProLiant DL360 G5 with QLogic/Emulex 4G dual-port HBAs.
>>  These servers have multipath connection to the storage system HP 3PAR 7200.
>>
>>  Before installing oVirt to servers I set up the configuration file /etc/multipath.conf according to the vendor recommendations from document "HPE 3PAR Red Hat Enterprise Linux and Oracle Linux Implementation Guide (emr_na-c04448818-9.pdf)"
>>  https://blog.it-kb.ru/2016/06/12/configuring-device-mapper-multipathing-dm-multipat-mpio-in-centos-linux-7-2-with-emulex-and-qlogic-fc-hba-connecting-over-san-storage-hp-3par-7200-3par-os-3-2-2/
>>
>>  Before installing oVirt my multipath.conf was the:
>>
>>  ---> start of /etc/multipath.conf <-----
>>
>>  defaults {
>>          polling_interval 10
>
> This will cause delays in path checking, better use the default from vdsm conf
>
>>          user_friendly_names no
>>          find_multipaths yes
>
> This ensures that devices with single path will not be detected by ovirt, unless
> the device is listed in the "multipaths" section. This means you will have to
> update multipath.conf manually on all hosts each time you want to add
> a new device.
> It is recommended to keep the default from vdsm.conf
>
>>  }
>>  blacklist {
>>          devnode "^cciss\/c[0-9]d[0-9]*"
>
> Not sure why you need this, but this seems harmless
>
>>  }
>>  multipaths {
>>         multipath {
>>                 wwid 360002ac000000000000000160000cec9
>>                 alias 3par-vv2
>>         }
>>         multipath {
>>                 wwid 360002ac000000000000000170000cec9
>>                 alias 3par-vv1
>>        }
>>  }
>>  devices {
>>          device {
>>                  vendor "3PARdata"
>>                  product "VV"
>>                  path_grouping_policy group_by_prio
>>                  path_selector "round-robin 0"
>>                  path_checker tur
>>                  features "0"
>>                  hardware_handler "1 alua"
>>                  prio alua
>>                  failback immediate
>>                  rr_weight uniform
>>                  no_path_retry 18
>
> This means 18 retries, and with polling internal of 10 seconds, 180 second
> timeout when all paths has become faulty. This will cause long timeouts in
> various vdsm operations, leading to timeouts on engine side, and also
> increase the chance of a host becoming non-operational because of delay
> in storage monitoring.
>
> It is recommended to use small number of retries, like 4, to avoid long delays
> in vdsm.
>
>>                  rr_min_io_rq 1
>>                  detect_prio yes
>>          }
>>  }
>>  ---> end of /etc/multipath.conf <-----
>>
>>  But after installing oVirt file multipath.conf has changed to:
>>
>>  ---> start of /etc/multipath.conf <-----
>>  defaults {
>>      polling_interval 5
>>      no_path_retry fail
>
> You can change this to small number like 4, to match other configuration.
>
>>      user_friendly_names no
>>      flush_on_last_del yes
>>      fast_io_fail_tmo 5
>>      dev_loss_tmo 30
>>      max_fds 4096
>
> You should keep these values, unless the storage vendor has
> a good reason to change them.
>
>>  }
>>  devices {
>>      device {
>>          all_devs yes
>>          no_path_retry fail
>
> I would change this to:
>
>     no_path_retry 4
>
>>      }
>>  }
>>  ---> end of /etc/multipath.conf <-----
>>
>>  Now I'm not sure that this configuration is optimal. What do you advise?
>
> 1. Add your changes to the file created by vdsm
> 2. Update no_path_retry to small number (e.g 4)
> 3. Add "# VDSM PRIVATE" to the second line - the first 2 lines should be:
>
> # VDSM REVISION 1.2
> # VDSM PRIVATE
>
> With the "# VDSM PRIVATE" tag, vdsm will never overwrite multipath.conf.
> You need to update this file on all hosts manually.
>
> 4. Copy multipath.conf to all hosts
> 5. Reload multipathd on all hosts:
>
>     systemctl reload multipathd
>
> Nir