Hi,
the path_grouping_policy is only responsible for the path grouping.
The "emc" prioritizer here, attributes a prio to each path.
Priorities of paths in the same group are aggregated into a pathgroup priority.
The pathgroup with the highest priority is activated.
Best regards,
Christophe Varoqui
On Tue, Mar 8, 2016 at 1:03 PM, Bernd Broermann <bernd@xxxxxxxxxxxxx> wrote:
Hello,
Does "group_by_serial" activate the "low latency" path ?
There are two servers which have a separate path to a EMC VPLEX box in different Data centers ( DC1 , DC2 ) .
Because of latency the paths are grouped by the serial number of the VPLEX box.
DC1 DC2
+------------+ +------------+
| Server 1 | | Server 2 |
+------------+ +------------+
| \ / |
| \ / |
| \ / |
| \ / |
| X |
| / \ |
| / \ |
| / \ |
| / \ |
+------------+ +------------+
|disk VPLEX A| |disk VPLEX B|
+------------+ +------------+
As I expected the paths are grouped and the path to the "nearest" disk( VPLEX) is active.
Is this an coincidence or does it work as designed ?
I didn't find something enlightening in the dm documentation.
Thank you for your help.
Bernd
partitial output of "multipathd show config"
....
device {
vendor "EMC"
product "Invista"
product_blacklist "LUNZ"
path_grouping_policy group_by_serial
getuid_callout "/lib/udev/scsi_id --whitelisted --device=/dev/%n"
path_selector "round-robin 0"
path_checker tur
features "0"
hardware_handler "1 emc"
prio emc
rr_weight uniform
no_path_retry fail
rr_min_io 1000
rr_min_io_rq 1
detect_prio yes
}
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