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Old 01-21-2009, 01:33 PM
Stephan Seitz
 
Default iscsi multipathed disks are slow

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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