iscsi multipathed disks are slow

[Stephan Seitz <stse+debian@fsing.rootsland.net>]

Hi!

I’m trying to connect a Dell server to an Eqlogic 5000E iSCSI device. The 
open-iscsi package is configured and working. Using the devices dd shows 
good results (~100MB/s for reading, ~85MB/s for writing) over one gigabit 
interface.

Using the multipath devices the numbers are only half as good (~50MB/s 
for reading) but now the system is using two gigabit interfaces.

Now I’m wondering why? Hints are welcome!

My configuration:
- Debian Lenny
- open-scsi 2.0.870~rc3-0.3
- multipath-tools 0.4.8-13
- dmsetup 2:1.02.27-4

Test kernels were the Lenny kernel (2.6.26-13) and a self-compiled 
2.6.28.1. The architecture is amd64.

The hardware is a Dell PowerEdge 1850 with two Intel Gigabit NICs onboard 
(Intel Corporation 82541GI Gigabit Ethernet Controller), MTU is set to 
9000.

/etc/multipath.conf:
blacklist {
devnode "^sda"
}

defaults {
  #path_grouping_policy group_by_prio
  path_grouping_policy multibus
  features "1 queue_if_no_path"
  path_checker readsector0
  failback immediate
  getuid_callout "/lib/udev/scsi_id -g -u -s /block/%n"
}

multipaths {
  multipath {
    wwid 36090a03820e51cc5d193945d00000007
    alias  my-lun0
  }
  multipath {
    wwid 36090a03820e56c17d193645d000020f0
    alias  my-lun1
  }
}

devices {
  device {
    vendor "EQLOGIC"
    product "5000E"
  }
}


multipath -ll shows:

my-lun1 (36090a03820e56c17d193645d000020f0) dm-8 ,
[size=1.0T][features=1 queue_if_no_path][hwhandler=0]
\_ round-robin 0 [prio=2][active]
 \_ #:#:#:# sdd 8:48  [active][ready]
 \_ #:#:#:# sde 8:64  [active][ready]
my-lun0 (36090a03820e51cc5d193945d00000007) dm-6 ,
[size=2.0T][features=1 queue_if_no_path][hwhandler=0]
\_ round-robin 0 [prio=2][active]
 \_ #:#:#:# sdc 8:32  [active][ready]
 \_ #:#:#:# sdb 8:16  [active][ready]


Using the same system with Windows Server OS, the multipath resulats are 
much better (~180MB/s for reading).

Shade and sweet water!

	Stephan

--
| Stephan Seitz             E-Mail: stse@fsing.rootsland.net |
| PGP Public Keys: http://fsing.rootsland.net/~stse/pgp.html |

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