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

[Peter Petrakis]

Then the only possible actors left are the actual initramdisk contents e.g.
zcat <initrd> | cpio -id  and examine all the scripts (init, conf/modules) to determine
how it could be loaded. The absence of the module reference in all of /etc and
/usr/share/initramfs-tools/ tell me that whatever is loading that module is doing
so as a side effect or an administration artifact e.g. someone wrote a udev rule and forgot.

Another possible source and this is also way out in left field is if modules.dep
was compromised and scsi_sh_rdac was added as dependency of another module 
and thus loaded indirectly.

root at nashira:/lib/modules/2.6.32-41-generic# grep scsi_dh modules*
modules.builtin:kernel/drivers/scsi/device_handler/scsi_dh.ko
modules.dep:kernel/drivers/scsi/device_handler/scsi_dh_rdac.ko:
modules.dep:kernel/drivers/scsi/device_handler/scsi_dh_hp_sw.ko:
modules.dep:kernel/drivers/scsi/device_handler/scsi_dh_emc.ko:
modules.dep:kernel/drivers/scsi/device_handler/scsi_dh_alua.ko:
Binary file modules.dep.bin matches
modules.order:kernel/drivers/scsi/device_handler/scsi_dh_rdac.ko
modules.order:kernel/drivers/scsi/device_handler/scsi_dh_hp_sw.ko
modules.order:kernel/drivers/scsi/device_handler/scsi_dh_emc.ko
modules.order:kernel/drivers/scsi/device_handler/scsi_dh_alua.ko
root at nashira:/lib/modules/2.6.32-41-generic# vim modules.dep
root at nashira:/lib/modules/2.6.32-41-generic# vim modules.builtin

Fine here.

concerning boot probe, scsi discovery is asymmetric, there's no expectation
of order. Performance tuning is where I get off, I also don't know much about
iSCSI transport, though yeah, jumbo frames it probably wise.

If you're seeing those messages before the file system is mounted then
the actors are definitely *in the ramdisk*, you just need to find them.

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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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