===== Multipath =====
Zakladni prikazy:
  * zobrazeni aktivnich multipathu: <code bash>multipath -ll</code>
  * reload podle kofigurace: <code bash>multipath -v2</code>
====Vzorova konfigurace====
  * nastavuje failover nad storage pripojnou pomoci FC a iSCSI
  * blacklistuje vsechna zarizeni mimo tech s wwid uvedenym v blacklist exceptions
  * multipathy uvadime v sekci multipaths, aby dostali hezke jmeno :)
<code json>
blacklist {
        wwid .*
}
blacklist_exceptions {
        property "(ID_WWN|SCSI_IDENT_.|ID_SERIAL)"
        wwid "26261353635663533|2317936357870636c"
}

defaults {
#                verbosity 6
                failback        manual
                path_grouping_policy  failover
                features "0"
                no_path_retry fail
}
multipaths {
       multipath {
              wwid              26261353635663533
              alias             backup
        }
       multipath {
              wwid              2317936357870636c
              alias             mach3
        }
}
</code>

====Pridani noveho multipath zarizeni====
  * pridavame zarizeni jehoz jedna z cest je /dev/sdh
  * zjistime si jeho scsi_id (wwid) nasledujicim prikazem: <code bash>/lib/udev/scsi_id -u -g -v /dev/sdh
2317936357870636c
</code>
  * pridame ho do konfigurace do sekce blacklist_exceptions (oddelovac je |):<code>wwid "26261353635663533|2317936357870636c"</code>
  * dale do sekce multipaths pridame jeho zaznam:<code>
multipath {
        wwid              2317936357870636c
        alias             mach3
}
</code>
  * nacteme konfiguraci:<code>
multipath -v2
create: mach3 (2317936357870636c) undef SCST_FIO,raid-disk
size=9.1T features='0' hwhandler='0' wp=undef
|-+- policy='service-time 0' prio=1 status=undef
| `- 1:0:2:1  sdh  8:112  undef ready running
`-+- policy='service-time 0' prio=1 status=undef
  `- 15:0:0:1 sdj  8:144  undef ready running
</code>
  * overime, ze multipath funguje:<code>
multipath -ll
backup (26261353635663533) dm-0 SCST_FIO,raid-disk
size=11T features='0' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=1 status=active
| `- 1:0:1:1  sddf 70:208 active ready running
`-+- policy='service-time 0' prio=1 status=enabled
  `- 14:0:0:1 sdm  8:192  active ready running
mach3 (2317936357870636c) dm-80 SCST_FIO,raid-disk
size=9.1T features='0' hwhandler='0' wp=rw
|-+- policy='service-time 0' prio=1 status=active
| `- 1:0:2:1  sdh  8:112  active ready running
`-+- policy='service-time 0' prio=1 status=enabled
  `- 15:0:0:1 sdj  8:144  active ready running</code>
  * vzniklo nam zarizeni /dev/mapper/mach3, ktere pouzivame stejne jako jakekoli jine blokove zarizeni

====Manual failover====
1) vyradit jednu z cest
<code bash>
echo offline > /sys/block/ [device name] /device/state
</code>
2) cestu vratit zpet
<code bash>
echo running > /sys/block/ [device name] /device/state
</code>

Je to vhodne udelat po automatickem failover v pripade, ze se prepne cesta z fc na iscsi. Je nastaveno nevracet se zpet, takze zabitim aktivniho ISCSI donutime multipath zase zacit pouzivat FC