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[dm-devel] info on defaults and features key for 1750500



Hello,
I have an IBM DS6800 storage system that is identified as 1750500
[]# cat /proc/scsi/scsi
Attached devices:
...
Host: scsi1 Channel: 00 Id: 01 Lun: 00
  Vendor: IBM      Model: 1750500          Rev: .441
  Type:   Direct-Access                    ANSI SCSI revision: 05
...

My system is rh el 5U3 x86_64 and has two fc hba connected to two fc
switches (connected then to the 4 ports of the storage system).
sw version is device-mapper-multipath-0.4.7-23.el5

I have a doubt about default configuration.
In this moment:
in multipath.conf no particular setting about the storage model. I only have

defaults {
        user_friendly_names yes
}

Under /usr/share/doc/device-mapper-multipath-0.4.7
multipath.conf.defaults says:
#defaults {
#       udev_dir                /dev
#       polling_interval        5
#       selector                "round-robin 0"
#       path_grouping_policy    failover
#       getuid_callout          "/sbin/scsi_id -g -u -s /block/%n"
#       prio_callout            none
#       path_checker            readsector0
#       rr_min_io               1000
#       rr_weight               uniform
#       failback                manual
#       no_path_retry           fail
#       user_friendly_names     no
#       bindings_file           "/var/lib/multipath/bindings"
#}

and
#       device {
#               vendor                  "IBM"
#               product                 "1750500"
#               getuid_callout          "/sbin/scsi_id -g -u -s /block/%n"
#               prio_callout            "/sbin/mpath_prio_alua %d"
#               features                "1 queue_if_no_path"
#               hardware_handler        "0"
#               path_grouping_policy    group_by_prio
#               failback                immediate
#               rr_weight               uniform
#               rr_min_io               1000
#               path_checker            tur
#       }

multipath.conf.annotated says
#       # name    : no_path_retry
#       # scope   : multipath & multipathd
#       # desc    : tell the number of retries until disable queueing, or
#       #           "fail" means immediate failure (no queueing),
#       #           "queue" means never stop queueing
#       # values  : queue|fail|n (>0)
#       # default : (null)
#       #
#       #no_path_retry  queue


two questions:
1) what is the meaning of the line
features                "1 queue_if_no_path"
? I didn't find anything about the "features" key.....
Is it the same as "no_path_retry=queue" ?

2) If the answer to 1) is no, taking for good the defaults above, does
this mean that in a default config I have on my system
no_path_retry           fail
?

Is there a command where I can see the actual config ?
(if for example anyone wants to cross check defaults written in docs
and real code behaviour)

Thanks in advance,
Gianluca


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