[Bug 1057054] Re: poor performance after upgrade to Precise

[Chris Weiss]

My devices are on iscsi, and I'm not booting off them.  They are not
connected until after the root goes live and network comes active, via
normal means.

I never manually loaded scsi_dh_rdac before, it's not in my initrd nor
my modules files.  It loaded automatically somehow.  Why isn't it
loading automatically earlier?  What loaded it if multipath driver
didn't?  other drivers load child drivers, why can't multipath?

I never found that html server guide in my searching and it is helpful.
The PDF I only found after failing a couple times.  Other software
presents prompts and links when config formats change, or even changes
them for you, it's become expected, multipath should do it too.  The
local manpage for multipath.conf still has prio_callout and not prio
documented, and has zero mention of having to manually load drivers.

Whether this a bug in how the drivers get loaded, or how the
documentation is presented, or how upgrade transition is handled isn't
that relevant, it's still a bug.  It's Lucid to Precise upgrade
regression bug.  it's not smooth and it's not even easy to find why it's
failing.

If the upgrade had presented me with a screen saying the config and
driver loading formats have changed, and that html link, I'd have
figured it out and we wouldn't be here.

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https://bugs.launchpad.net/bugs/1057054

Title:
  poor performance after upgrade to Precise

Status in “multipath-tools” package in Ubuntu:
  Invalid

Bug description:
  I had a Lucid x64 server working with a Dell MD3000i with 4 paths and
  worked as expected.  I added the "prio rdac" line to the conf file,
  then upgraded to Precise, and removed the old mpath_rdac line and
  reboot one more time, just to be sure.  I did this based on a section
  in https://help.ubuntu.com/12.04/serverguide/serverguide.pdf

  as a "sanity check" test, I'm doing 'pv < /dev/mapper/dellsas1 >
  /dev/null' (friendly names enabled).  On Lucid i'd get about 100MB/s
  After upgrading to Precise I get an almost solid 768kB/s.  If I
  instead use the 4 underlying /dev/sd* devices, 2 give errors as
  expected, and 2 run at about 100MB/s as expected so iscsi seems to be
  working correctly and multipath not.

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