The preffered path means, that it's not entirely an Active/Active
configuration.
You probably have LUNs on both controllers – and - system can see LUNs
thru both of them, but only one path (controller) is ready to be active
and send/receive data.
Before RHEL 5 you should use IBM RDAC driver (configuration was simple).
Now RDAC implementation is in device-multipathing.
You should see the the
/usr/share/doc/device-mapper-multipath-0.4.7/multipath.conf.defaults and
look for device configuration:
device {
vendor "IBM"
product "1722-600"
[…]
}
We currently use:
device {
# for DS4700
vendor "IBM"
product "1722-600"
prio_callout "/sbin/mpath_prio_rdac /dev/%n"
features "1 queue_if_no_path"
hardware_handler "1 rdac"
failback immediate
rr_weight uniform
no_path_retry 300
path_checker rdac
}
With defaults:
defaults {
udev_dir /dev
getuid_callout "/sbin/scsi_id -g -u -s /block/%n"
path_checker rdac
rr_min_io 1000
max_fds 8192
user_friendly_names yes
}
The preffered path is changed by a array if there is no way to use the
chosen prefferd path. RHEL is choosing the right path with the priorities
(prio_callout "/sbin/mpath_prio_rdac /dev/%n").
BTW:
You can have all active paths on DS8xxx but not on DS4xxx series.
Best Regards
Krzysztof Mazurek
[email protected] — zapisano w dniu 2009-07-08 14:32:55:
> Win Htin <[email protected]>
> Wysłane przez: [email protected]
>
> 2009-07-08 14:32
>
> Odpowiedz użytkownikowi
> "Red Hat Enterprise Linux 5 \(Tikanga\) discussion mailing-list"
> <[email protected]>
>
> Do
>
> [email protected]
>
> DW
>
> Temat
>
> [rhelv5-list] Dynamic Multipathing boot disks - Part 2
>
> Hi folks,
>
> Thanks to Tom's help, I have Dynamic Multipathing up and running for
> my boot disks.
>
> My next question is, how can I configure the boot disk to stay on the
> controller that I specify? Currently, the Storage Array (IBM DS4700,
> Active/Active controllers) starts complaining the logical drive is not
> on preferred path (controller A). If I change the preferred path back
> to controller A, it immediately goes back to controller B. For the
> other servers, I have modified QLogic driver installed kernels and
> assign preferred paths through qlremote/SanSurfer combo.
>
> Your help is much appreciated. TIA.
>
> Cheers,
> Win
>
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