VxVM 4.1 specifics


Third-party driver coexistence



5.0 (MP1) DMP COEXISTENCE WITH EMC POWERPATH

      ■   If you are installing VxVM 5.0 and PowerPath is installed, you no longer need to download the CLARiiON ASL and its associated APM. Both components are installed by default. The CLARiiON array must be configured in explicit fail-over mode. Failover Mode “1”

     ■ If you are installing VxVM 5.0 and PowerPath is NOT installed.. The CLARiiON array can be configured in either mode (1 or 2). Support would now recommend Failover Mode “1” with both DMP and PowerPath , as circumstances have since changed.

libvxemc.so                           = Claims EMC Symmetrix /DMX luns
libvxCLARiiON.so                = Claims EMC CLARiiON luns

     ■ When PowerPath is configured, all the EMC array type luns are claimed by the libvxemc.so ASL.

VxVM 5.0 MP3 introduced the "libvxpp.so" TPD ASL


• With the SF 5.0 MP3 release of VxVM , DMP can co-exist with PowerPath . Both the “ libvxemc.so and “ libvxCLARiiON.so ” ASL’s are installed by default as before. The EMC CLARiiON APM “ dmpCLARiiON ” is also installed by default as before.

     ■ The key change is the introduction of the " libvxpp.so " ASL library which handles the TPD (Third Party Driver) claiming mechanism for PowerPath controlled LUNS.

      ■   As with 5.0, if you are installing VxVM 5.0 and PowerPath is installed, you no longer need to download the CLARiiON ASL and its associated APM. Both components are installed by default. The CLARiiON array must be configured in explicit fail-over mode “1” or "4" depending on the CLARiiON FlareCode and 5.0 MP3 RP patch level.

- If 5.0 MP3 RP1 has been installed; Failover Mode “4” (ALUA) can be set for both PowerPath and DMP. The EMC CLARiiON Flare Code must be a minimum of “26” or higher


libvxemc.so                           = Claims EMC Symmetrix /DMX luns
libvxCLARiiON.so                = Claims EMC CLARiiON luns
libvxpp.so                             = Claims EMC PowerPath managed luns          (NEW)

   

  ■ When PowerPath is configured, all the PowerPath managed/controlled (TPD) EMC array type luns are claimed by the libvxpp.so ASL.

- To allow DMP to receive correct enquiry data from EMC Symmetrix/DMX disk arrays, the common Serial Number (C-bit) Symmetrix Director parameter must be set to enabled.





DMP tunable "dmp_fast_recovery"


The "dmp_fast_recovery" tunable does not add any value in PowerPath environments as the device is below the DMP device and is not a SCSI device.

Configurations involving DMP (Dynamic Multipathing) and other Third Party Drivers (TPD) like Sun's MPxIO and EMC's Powerpath effectively reduces the number of paths DMP operates on, to a single path.

EMC Powerpath is a path non-suppressing driver (DMP sees the PP meta-device and the OS native device paths) and DMP operates on the PP meta-device which in turn operates on the OS native device paths.


5.0 code change

A code change was implemented with SF 5.0 to automatically skip the "dmp_fast_recovery" operation for PowerPath devices. The "dmp_fast_recovery" would be shown as "ON" in gettune CLI as it's a global setting, however, DMP will automatically bypass the "dmp_fast_recovery" code path for PP devices

 

# vxdmpadm gettune all
Tunable Current Value Default Value
------------------------------ ------------- -------------
dmp_failed_io_threshold  57600 57600
dmp_retry_count  5 5
dmp_pathswitch_blks_shift  9 9
dmp_queue_depth  32 32
dmp_cache_open  on on
dmp_daemon_count  10 10
dmp_scsi_timeout  30 30
dmp_delayq_interval  15 15
dmp_path_age  300 300
dmp_stat_interval  1 1
dmp_health_time  60 60
dmp_probe_idle_lun  off on
dmp_log_level  1 1
dmp_fast_recovery  on on
dmp_enable_restore  on on
dmp_low_impact_probe  on on
dmp_probe_threshold  5 5
dmp_restore_policy  check_disabled check_disabled
dmp_restore_interval  300 300
dmp_restore_cycles  10 10
dmp_sfg_threshold  1 1
dmp_lun_retry_timeout  0 0
dmp_native_multipathing  off off
dmp_monitor_fabric  on on

DMP internally detects that a given device is a PowerPath device (the enclosure is claimed by the corresponding PowerPath ASL and is marked with DA_TPD flag)

The dmp_send_scsipkt function skips the dmp_fast_recovery code path if the device represents a TPD device.

The tunable is turned ON globally for other non TPD devices, as the environment may exist of both PowerPath controlled devices and other enclosures controlled by DMP for which are doing selective multipathing on the same host. In this case DMP would use the "dmp_fast_recovery" mechanism for the devices where it controls the multipathing, and skip those where the devices are handled by PowerPath.



DMP tunable "dmp_proble_idle_lun"


Etrack 1833006 has been resolved in 5.1 SP1, where DMP will no longer probe idle PP devices.

Whilst the "dmp_probe_idle_lun" tunable is enabled, the dmpevents.log file gets flooded with "Marked as idle Path" messages:


Sample messages

# cat /etc/vx/dmpevents.log
Wed Feb 17 08:53:01.270: Marked as idle Path emcpower4s2 belonging to Dmpnode emcpower4s2
Wed Feb 17 08:53:01.270: Marked as idle Path emcpower1s2 belonging to Dmpnode emcpower1s2
Wed Feb 17 08:53:01.270: Marked as idle Path emcpower7s2 belonging to Dmpnode emcpower7s2
Wed Feb 17 08:53:01.270: Marked as idle Path emcpower5s2 belonging to Dmpnode emcpower5s2
Wed Feb 17 08:53:01.270: Marked as idle Path emcpower6s2 belonging to Dmpnode emcpower6s2
Wed Feb 17 08:53:01.270: Marked as idle Path emcpower17s2 belonging to Dmpnode emcpower17s2
Wed Feb 17 08:53:01.270: Marked as idle Path emcpower20s2 belonging to Dmpnode emcpower20s2
Wed Feb 17 08:53:01.270: Marked as idle Path emcpower16s2 belonging to Dmpnode emcpower16s2
Wed Feb 17 08:53:02.270: Marked as idle Path emcpower4s2 belonging to Dmpnode emcpower4s2
Wed Feb 17 08:53:02.270: Marked as idle Path emcpower1s2 belonging to Dmpnode emcpower1s2
Wed Feb 17 08:53:02.270: Marked as idle Path emcpower7s2 belonging to Dmpnode emcpower7s2
Wed Feb 17 08:53:02.270: Marked as idle Path emcpower5s2 belonging to Dmpnode emcpower5s2
Wed Feb 17 08:53:02.270: Marked as idle Path emcpower6s2 belonging to Dmpnode emcpower6s2
Wed Feb 17 08:53:02.270: Marked as idle Path emcpower17s2 belonging to Dmpnode emcpower17s2
Wed Feb 17 08:53:02.270: Marked as idle Path emcpower20s2 belonging to Dmpnode emcpower20s2
Wed Feb 17 08:53:02.270: Marked as idle Path emcpower16s2 belonging to Dmpnode emcpower16s2

This is because the I/O does not go through DMP; therefore, DMP thinks the paths are idle. It should be a one-off message for each path.


Note: The user no longer needs to disable the "probe_idle_lun" tunable with VxVM 5.1 SP1.


VxVM 5.1 SP1 excludes PowerPath(PP) controlled (TPD) devices from the idle lun probing logic, and therefore the "idle lun events" would no longer be reported for PP related devices.


vxesd

Eventsource daemon

Volume Manager's(VM) Dynamic MultiPathing (DMP) driver has been compatibility tested for co-existence with multiple Third Party (Multipathing) Driver (TPD) like EMC Corporation's Powerpath , Sun Microsystems' StorEdge Traffic Manager(STMS) also know as MPxIO, IBM Corporation's System Storage Multipath Subsystem Device Driver (SDD).

Software configurations involving DMP and any one of the TPD mentioned above, during dynamic lun addition, exhibit an anomalous behavior wherein vxdisk list output following execution of the command vxdctl enable will result in ghost or duplicate entries. The inconsistency is benign in nature. The cause of this anomaly is due to the lun being recognized by the event source daemon ( which is responsible for passing disk information to the Device Discovery layer (DDL) ) causing a DMP node to be created prior to the TPD claiming the device. Once the TPD correctly claims the device via the ASL another DMP metanode will be created resulting in duplicate entries represented in the vxdisk list output.

Until 5.1 SP1 Symantec would recommend disabling the "vxesd" eventsource daemon where PowerPath is installed.


Disabling vxesd will come at some cost. The below events will be handled in a delayed manner:

1. OS reconfiguration events

2. DMP events for ISIS in the absence of VOLD

3 . VOLD(DMP) events for Logging/Processing

4 . HBA API events for proactive error detection by DMP

When planning to stop the vxesd process, make sure the restore daemon value (by default is 300 seconds) is 5 minutes or less to help minimize the delay of dmp event triggered by the vxdmpadm start restore interval= attribute.


Note: 5.1 SP1 disables vxesd automatically when EMC  PowerPath is detected.



DMP Improvement in 5.0 MP3 RP2 (Solaris)


DMP enhancement to handle failing IO when it is not able to interpret sense data( without fix possible side effects like dgdisabled diskgroups, disk failures)
https://www.symantec.com/business/support/index?page=content&id=000042175