Multipath and Xenserver?

Does the DSS support iscsi multipathing from xen servers, and if so, will this work in failover with 2xdss servers?

Each Xen node has 2xGE dedicated to iSCSI and the DSS servers each have 6xGE for iSCSI traffic, and 2xGE for replication traffic. We initially had the 6xGE setup in a bond and had a bond on the Xenserver side, and we are now being told we would get better performance if we used multipathing on the Xen side. To do this on the DSS server side however, we need to create multiple single GE targets and not use bonding, or create multiple smaller # of GE bonds, since the xen server has to see multiple paths via iSCSI for it to work.

This possible on the DSS side, and if so, do you agree performance would be better?

Thanks in advance!
Tom

Hi Tom - Currently we don’t have any doc's on the XEN systems only with the Virtual Iron from the link below on how to set this up. This was given to us by one of our customers.

For MPIO with Microsoft we have a short how to that explains that each NIC must be on a separate subnet this is all that is needed to do on our end. If you have many NIC's in the system you can bond 2 NICs to create one subnet then repeat for the other.

Todd,

Thanks! No link provided, can you send it to me?

Basically from my testing/researching last night, I'm not sure DSS will support this for Xen or VMWare (btw Virtual Iron is based on Xen I thought?).

Basically I needs to see the LV/LUN on multiple iSCSI targets, and in DSS I cannot map a Lv/LUN to multiple targets, is this correct?

From the Xenserver docs:

3.3.10. Storage Multipathing

Dynamic multipathing support is available for Fibre Channel and iSCSI storage backends. By default, it uses round-robin mode load balancing, so both routes will have active traffic on them during normal operation. Multipathing can be enabled in XenCenter or on the command line.
Caution

Before attempting to enable multipathing, verify that multiple targets are available on your storage server. For example, an iSCSI storage backend queried for sendtargets on a given portal should return multiple targets, as in the following example:

iscsiadm -m discovery --type sendtargets --portal 192.168.0.161
192.168.0.161:3260,1 iqn.strawberry:litchie
192.168.0.204:3260,2 iqn.strawberry:litchie

Link for the Virtual Iron setup.

http://www.open-e.com/library/product-presentations/

Library
Product Presentations

Open-E in Virtual Appliances

2009 - Multipath with Virtual Iron and Open-E Data Storage Server, December 2008

You are correct that when setting up a LUN it is for the Target that you wish to assign for only.

im fooling a bit with xenserver, it seems like open-e really dosnt report multiple paths to the target, but there is a little manual workaround

first my device in multipath.conf:


device {
vendor "iSCSI"
product "*"
path_grouping_policy multibus
path_checker tur
features "1 queue_if_no_path"
failback immediate
rr_min_io 1000 # try different values, for me 4 seems to work best
path_selector "round-robin 0"
}

since xen allows only to setup one connection to a specific lun, you have to setup another connection manually, for example:
- iscsi target (open-e) on 192.168.0.1/24 and 192.168.1.1/24
- in xencenter activate multipath
- setup SR to 192.168.0.1
- login to xen via ssh
- iscsi login to the 192.168.1.1:
"iscsiadm --mode discovery --type sendtargets --portal 192.168.1.1
iscsiadm --mode node --targetname iqn.2009-04:dss.target0 --portal 192.168.1.1 --login"

at this moment xencenter should report 2 active paths to the SR.. well there should be a way to make it automatic but didnt see in to it yet, also i would suggest to read dm-multipath manual

I tired, but xenserver still says only 1 of 1 multipaths:

Login session [iface: default, target: iqn.2010-05:iscsi.target0, portal: 172.16.32.200,3260]
Login session [iface: default, target: iqn.2010-05:iscsi.target0, portal: 172.16.31.200,3260]
[root@Unix02 ~]# multipath -ll
200000000d11ba481dm-3 SCST_FIO,0a1Fm75r3fC3oD
[size=5.4T][features=1 queue_if_no_path][hwhandler=0]
\_ round-robin 0 [prio=1][active]
\_ 12:0:0:0 sdc 8:32 [active][ready]
SATA_ST31000340NS_9QJ39EV2dm-0 ATA,ST31000340NS
[size=932G][features=0][hwhandler=0]
\_ round-robin 0 [prio=1][active]
\_ 1:0:0:0 sdb 8:16 [active][ready]
[root@Unix02 ~]#


[root@Unix02 ~]# /etc/init.d/multipathd restart
Stopping multipathd daemon: [ OK ]
Starting multipathd daemon: [ OK ]
[root@Unix02 ~]# multipath -ll
200000000d11ba481dm-3 SCST_FIO,0a1Fm75r3fC3oD
[size=5.4T][features=1 queue_if_no_path][hwhandler=0]
\_ round-robin 0 [prio=2][enabled]
\_ 12:0:0:0 sdc 8:32 [active][ready]
\_ 13:0:0:0 sdd 8:48 [active][ready]
SATA_ST31000340NS_9QJ39EV2dm-0 ATA,ST31000340NS
[size=932G][features=0][hwhandler=0]
\_ round-robin 0 [prio=1][active]
\_ 1:0:0:0 sdb 8:16 [active][ready]
[root@Unix02 ~]#




I added the following config:
# BARRY ADDED
device {
vendor "iSCSI"
product "*"
path_grouping_policy multibus
path_checker tur
features "1 queue_if_no_path"
failback immediate
rr_min_io 4 # try different values, for me 4 seems to work best
path_selector "round-robin 0"
}

device {
vendor "SCST_FIO"
product "*"
path_grouping_policy multibus
path_checker tur
features "1 queue_if_no_path"
failback immediate
rr_min_io 4 # try different values, for me 4 seems to work best
path_selector "round-robin 0"
}


And also:
multipaths {
multipath {
wwid 200000000d11ba481dm-2
alias multipath2
}

Any help would be appreciated.

thanks
Barry

In addition here is a verbose output:

sdc: not found in pathvec
sdc: mask = 0x5
sdc: bus = 1
sdc: dev_t = 8:32
sdc: size = 11702837248
sdc: vendor = SCST_FIO
sdc: product = 0a1Fm75r3fC3oDLw
sdc: rev = 101
sdc: h:b:t:l = 12:0:0:0
sdc: path checker = tur (controller setting)
sdc: state = 2
sdd: not found in pathvec
sdd: mask = 0x5
sdd: bus = 1
sdd: dev_t = 8:48
sdd: size = 11702837248
sdd: vendor = SCST_FIO
sdd: product = 0a1Fm75r3fC3oDLw
sdd: rev = 101
sdd: h:b:t:l = 13:0:0:0
sdd: path checker = tur (controller setting)
sdd: state = 2
===== paths list =====
uuid hcil dev dev_t pri dm_st chk_st vend/prod/rev
0:0:0:0 sda 8:0 0 [undef][ready] ATA,ST3500641AS
1:0:0:0 sdb 8:16 0 [undef][ready] ATA,ST31000340NS
12:0:0:0 sdc 8:32 0 [undef][ready] SCST_FIO,0a1Fm75r3fC3oDLw
13:0:0:0 sdd 8:48 0 [undef][ready] SCST_FIO,0a1Fm75r3fC3oDLw
params = 1 queue_if_no_path 0 1 1 round-robin 0 2 1 8:32 4 8:48 4
status = 2 0 0 0 1 1 A 0 2 0 8:32 A 0 8:48 A 0
sdc: mask = 0x8
sdc: getprio = NULL (internal default)
sdc: prio = 1
sdd: mask = 0x8
sdd: getprio = NULL (internal default)
sdd: prio = 1
200000000d11ba481dm-3 SCST_FIO,0a1Fm75r3fC3oD
[size=5.4T][features=1 queue_if_no_path][hwhandler=0]
\_ round-robin 0 [prio=2][active]
\_ 12:0:0:0 sdc 8:32 [active][ready]
\_ 13:0:0:0 sdd 8:48 [active][ready]
params = 0 0 1 1 round-robin 0 1 1 8:16 5
status = 2 0 0 0 1 1 A 0 1 0 8:16 A 0
sdb: mask = 0x8
sdb: getprio = NULL (internal default)
sdb: prio = 1
SATA_ST31000340NS_9QJ39EV2dm-0 ATA,ST31000340NS
[size=932G][features=0][hwhandler=0]
\_ round-robin 0 [prio=1][active]
\_ 1:0:0:0 sdb 8:16 [active][ready]