On Fri, 2009-08-07 at 15:25 -0500, Akshay Lal wrote:
> I'm having a few issues with path priorities. It seems that the choice
> of path to use during I/O is independent of the user defined priorities
> for each path.
>
> I am setting the priorities by executing writing a script that is used
> by prio_callout. This seems to work when I execute multipath -ll since
> all the specified priorities show up correctly. (the
> path_grouping_policy being used is failover)
>
> multipath -ll:
> --------------
> mpath2 (244534e3833623961) dm-1 DSNET,Dispersed Store
> [size=47G][features=1 queue_if_no_path][hwhandler=0][rw]
> \_ round-robin 0 [prio=10][enabled]
> \_ 85:0:0:0 sdc 8:32 [active][ready]
> \_ round-robin 0 [prio=5][enabled]
> \_ 87:0:0:0 sde 8:64 [active][ready]
> mpath1 (244534e3266616134) dm-0 DSNET,Dispersed Store
> [size=47G][features=1 queue_if_no_path][hwhandler=0][rw]
> \_ round-robin 0 [prio=5][enabled]
> \_ 84:0:0:0 sdb 8:16 [active][ready]
> \_ round-robin 0 [prio=10][enabled]
> \_ 86:0:0:0 sdd 8:48 [active][ready]
>
> At this point when I dd to /dev/mapper/mpath1 or /dev/mapper/mpath2 the
> priorities don't come into play at all. Data starts going to /dev/sdc
> for /dev/mapper/mpath2 & /dev/sdb for /dev/mapper/mpath1, which totally
> by-passes the set priorities. Below is a list of all the conf files and
> scripts I'm using.
>
>
>
> /etc/multipath.conf
> --------------------
> defaults {
> udev_dir /dev
> polling_interval 1
> selector "round-robin 0"
> path_grouping_policy multibus
> getuid_callout "/sbin/scsi_id -g -u -s /block/%n"
> prio_callout "/bin/bash
> /root/MultipathScripts/mpath_prio_alt %n"
> path_checker tur
> rr_min_io 128
> max_fds 8192
> rr_weight priorities
> failback immediate
> no_path_retry queue
> user_friendly_names yes
> }
>
>
> /root/MultipathScripts/mpath_prio_alt :
> ---------------------------------------
> #!/bin/bash
> # if not passed any device name, return a priority of 0
> if [ -z "${1}" ];then
> echo 0
> exit
> fi
>
> ENTRY="$(ls -l1 /dev/disk/by-path | grep /${1}'$')"
> DEV="${ENTRY##* ip-}"
> if [ "$DEV" = "${ENTRY}" ];then #This is not an iSCSI device
> echo 0
> exit
> fi
>
> # stripping $ENTRY to obtain the IP:Port-iscsi-iqn-lunNumber
> DEV="${ENTRY##* ip-}"
> #DEV="${DEV%% ->*}" # the pattern changed in CentOS 5.3
> #DEV="$(echo ${DEV} | sed 's/-lun-[0-9][0-9]* ->.*//')"
> DEV="${DEV%%-lun-[0-9]* ->*}"
>
> echo $(grep ${DEV} /root/MultipathScripts/iscsi.list | cut -f2)
>
>
> /root/MultipathScripts/iscsi.list:
> ----------------------------------
> 192.xxx.xxx.103:3260-iscsi-iqn.2008-07.com.company:stoarge-2 1
> 192.xxx.xxx.106:3260-iscsi-iqn.2008-07.com.company:stoarge-2 0
> 192.xxx.xxx.103:3260-iscsi-iqn.2008-07.com.company:stoarge-1 0
> 192.xxx.xxx.106:3260-iscsi-iqn.2008-07.com.company:stoarge-1 1
>
>
> Is there something I'm doing wrong? I would like to be able to define
> the priorities per device, and ensure that data only traverses on the
> lower priority path when
> a) a failure to the first path (path with a higher priority) occures
> b) no other path with a higher priority exists
<snip>
I believe to do what you want you will need two changes. First, set
path_grouping_policy to failover.
Second, multipathd needs to have everything in memory so not only do you
need /bin/bash loaded into memory (via your prio-callout line in
defaults) but you must also load your script into memory. We did this
with a dummy device. Here is our devices section of multipath.conf:
devices {
device {
vendor "NEXENTA"
product "COMSTAR"
getuid_callout "/sbin/scsi_id -g -u -s /block/%n"
features "0"
hardware_handler "0"
# path_grouping_policy failover
rr_weight uniform
# rr_min_io 1000
path_checker tur
}
device {
vendor "dummy"
product "Used_to_load_mpath_prio_ssi_into_memory"
prio_callout "/sbin/mpath_prio_ssi %n"
}
}
Hope this helps - John
--
John A. Sullivan III
Open Source Development Corporation
+1 207-985-7880
jsullivan@xxxxxxxxxxxxxxxxxxx
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