Function of leg_mpath_enable attribute of scsimgr

[stephen peng]

Guys,

I've got a EMC Lun usage issue on HP-UX platform, pvcreate and diskinfo was ok for this specific LUN, but when I tried to create a VG using this LUN, there came an error:

#vgcreate -s 32 /dev/gdc /dev/disk/disk24
Increased the number of physical extents per physical volume to 4799.
vgcreate: Volume group "/dev/gdc" could not be created:
Unable to read the physical volume.

But when I run

scsimgr save_attr -a leg_mpath_enable=0

it was ok to execute vgcreate to this LUN.

So could some one explain this attribute of scsimgr to me under such situation.

regards

Stephen

[Patrick Wallek]

From the scsimgr man page:

Attribute Name        RO/RW Type     Description
----------------------------------------------------------------
leg_mpath_enable      RW    boolean  Default setting of
                                     tunable to enable or
                                     disable multi-pathing on
                                     legacy DSF of a LUN.
                                     Values: false (0) or
                                     true (1).

[Torsten.]

from manual:

leg_mpath_enable is an attribute which controls whether built-in multi-pathing is enabled when a device is accessed through a legacy DSF. This tunable can be set at a global level or for a particular LUN. By default the SCSI stack explicitly sets this attribute to true at the global level to enable by default multi-pathing for legacy DSFs of all LUNs.




Hmmm, should not apply if you use the agile device ...

[stephen peng]

Torsten,

Before scsimgr was executed, vgcreate with legacy dsf failed either with the same warning.

regards

Stephen

[Torsten.]

This is IMHO strange.

Let's assume disk100 is also c1t0d0 and c2t0d0.

By accessing disk100 you are using the default multipathing mode.

Same for accessing c1 or c2t0d0 by default.

Only with this attribute disabled c1t0d0 is accessing only this refering path, no multipath behaviour.


Maybe there is a problem with your EMC configuration settings? Not the correct values for hp-ux?

Please post also

# scsimgr get_info -D /dev/rdisk/disk24

[stephen peng]

Torsten,

FYI

>scsimgr get_info -D /dev/rdisk/disk24

        STATUS INFORMATION FOR LUN : /dev/rdisk/disk24

Generic Status Information

SCSI services internal state                  = ONLINE
Device type                                   = Direct_Access
EVPD page 0x83 description code               = 1
EVPD page 0x83 description association        = 0
EVPD page 0x83 description type               = 3
World Wide Identifier (WWID)                  = 0x600601601c820c0073df8a032236df11
Serial number                                 = "CK200031001584"
Vendor id                                     = "DGC     "
Product id                                    = "RAID 5          "
Product revision                              = "0219"
Other properties                              = ""
SPC protocol revision                         = 4
Open count (includes chr/blk/pass-thru/class) = 1
Raw open count (includes class/pass-thru)     = 4294967289
Pass-thru opens                               = 0
LUN path count                                = 2
Active LUN paths                              = 2
Standby LUN paths                             = 0
Failed LUN paths                              = 0
Maximum I/O size allowed                      = 2097152
Preferred I/O size                            = 2097152
Outstanding I/Os                              = 0
I/O load balance policy                       = round_robin
Path fail threshold time period               = 0
Transient time period                         = 120
Tracing buffer size                           = 1024
LUN Path used when policy is path_lockdown    = NA
LUN access type                               = NA
Asymmetric logical unit access supported      = No
Asymmetric states supported                   = NA
Preferred paths reported by device            = No
Preferred LUN paths                           = 0

Driver esdisk Status Information :

Capacity in number of blocks                      = 314572800
Block size in bytes                               = 512
Number of active IOs                              = 0
Special properties                                =
Maximum number of IO retries                      = 45
IO transfer timeout in secs                       = 30
FORMAT command timeout in secs                    = 86400
START UNIT command timeout in secs                = 60
Timeout in secs before starting failing IO        = 120
IO infinite retries                               = false

regards

Stephen