<div dir="ltr">Hi,<div><br></div><div>the <span style="font-size:19.2px">path_grouping_policy is only responsible for the path grouping.</span></div><div><span style="font-size:19.2px">The "emc" prioritizer here, attributes a prio to each path.</span></div><div><span style="font-size:19.2px">Priorities of paths in the same group are aggregated into a pathgroup priority.</span></div><div><span style="font-size:19.2px">The pathgroup with the highest priority is activated.</span></div><div><span style="font-size:19.2px"><br></span></div><div><span style="font-size:19.2px">Best regards,</span></div><div><span style="font-size:19.2px">Christophe Varoqui</span></div><div><span style="font-size:19.2px"><a href="http://www.opensvc.com">www.opensvc.com</a></span></div><div><span style="font-size:19.2px"><br></span></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Mar 8, 2016 at 1:03 PM, Bernd Broermann <span dir="ltr"><<a href="mailto:bernd@broermann.com" target="_blank">bernd@broermann.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello,<br>
<br>
<br>
Does "group_by_serial" activate the "low latency"  path ?<br>
<br>
There are two servers which have a separate path to a EMC VPLEX box in different Data centers ( DC1 , DC2 ) .<br>
<br>
Because of latency the paths are grouped by the serial number of the VPLEX box.<br>
<br>
<br>
<br>
<br>
       DC1                DC2<br>
<br>
   +------------+    +------------+<br>
   | Server 1   |    | Server 2   |<br>
   +------------+    +------------+<br>
      |   \              /  |<br>
      |     \          /    |<br>
      |       \      /      |<br>
      |         \  /        |<br>
      |          X          |<br>
      |        /   \        |<br>
      |      /       \      |<br>
      |    /           \    |<br>
      |  /              \   |<br>
   +------------+    +------------+<br>
   |disk VPLEX A|    |disk VPLEX B|<br>
   +------------+    +------------+<br>
<br>
<br>
As I expected the paths are grouped and the path to the "nearest" disk( VPLEX) is active.<br>
<br>
Is this an coincidence or does it work as designed ?<br>
<br>
I didn't find something enlightening in the dm documentation.<br>
<br>
Thank you for your help.<br>
<br>
Bernd<br>
<br>
<br>
<br>
partitial output of  "multipathd show config"<br>
....<br>
device {<br>
    vendor "EMC"<br>
    product "Invista"<br>
    product_blacklist "LUNZ"<br>
    path_grouping_policy group_by_serial<br>
    getuid_callout "/lib/udev/scsi_id --whitelisted --device=/dev/%n"<br>
    path_selector "round-robin 0"<br>
    path_checker tur<br>
    features "0"<br>
    hardware_handler "1 emc"<br>
    prio emc<br>
    rr_weight uniform<br>
    no_path_retry fail<br>
    rr_min_io 1000<br>
    rr_min_io_rq 1<br>
    detect_prio yes<br>
}<br>
<br>
--<br>
dm-devel mailing list<br>
<a href="mailto:dm-devel@redhat.com" target="_blank">dm-devel@redhat.com</a><br>
<a href="https://www.redhat.com/mailman/listinfo/dm-devel" rel="noreferrer" target="_blank">https://www.redhat.com/mailman/listinfo/dm-devel</a><br>
</blockquote></div><br></div>