NAS4FREE iSCSI Multipath

ASE001

ASE001

ASE001

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2 Jan 2007
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I'm trying to simulate a multipath connection to a SAN to test MPIO configurations on a Server 2008R2 build. The Srv2008 initiates the connection on both paths but I can only see the disk once? What I need is to see the same disk twice? Any ideas?

These are my current settings

Tag Portals Comment
2 1.1.2.1:3260
1.1.1.1:3260 iSCSI01

Tag Initiators Networks Comment
1 ALL 1.1.1.0/24
1.1.2.0/24 iSCSI01

Name Flags LUNs
iqn.ase.san:disk0 rw LUN0=/mnt/Data01/Data_tst_01.dsk
PG IG AG
2 1 none

Cheers
ASE001
 
oddjob62 said:
don't understand why you need/expect to see the disk twice.
Click to expand...

If the OS can see the same disk down two different paths (ie subnets), the OS should see the disk twice. Then you use MPIO (multipath I/O) which is part of Server 2008 Features that you can add to make the OS see it as a single drive.

It's all about High Availability systems, if one path fails then it uses the alternate path to the storage. NIC teaming is not recommended by Microsoft and they recommend a MPIO configuration for iSCSI. But never having used iSCSI in a production environment, only Fibre Channel I wanted to at least get familiar with the configuration.
 
Got it working by disabling each iSCSI NIC in turn, then in Disk Manager 'Rescan Disks' and then re-enable the NIC. The disk now appears twice although you can only bring one disk online at a time. The MS iSCSI initiator still only sees one target, not sure if this is correct or not, I need to think about this?

I then installed/enabled the MPIO feature from the server manage, then did a reboot.

I configured MPIO to support iSCSI which reported no errors after it did some automated configuration/discovery.

The second disk disappeared from Disk Manager as expected.

Disconnecting (disable iSCSI NIC) either of the iSCSI connections the disk still remains accessible.

I still need to do some testing, but it's looking good!
 
ASE001 said:
If the OS can see the same disk down two different paths (ie subnets), the OS should see the disk twice. Then you use MPIO (multipath I/O) which is part of Server 2008 Features that you can add to make the OS see it as a single drive.

It's all about High Availability systems, if one path fails then it uses the alternate path to the storage. NIC teaming is not recommended by Microsoft and they recommend a MPIO configuration for iSCSI. But never having used iSCSI in a production environment, only Fibre Channel I wanted to at least get familiar with the configuration.
Click to expand...

I know how MPIO works i've set up a dozen hyper-v clusters using it. I've never seen the same disk twice.

You only ever see 1 disk, because it's the same disk no matter which path you go down.
 
I more familiar with Fibre (HBS's) channel and you always see two disks in disk manager unless MPIO is installed. iSCSI should be the same and that's what I saw in my testing, although I had to jig it to work which I never had to do with Fibre channel.
 
ASE001 said:
I more familiar with Fibre (HBS's) channel and you always see two disks in disk manager unless MPIO is installed. iSCSI should be the same and that's what I saw in my testing, although I had to jig it to work which I never had to do with Fibre channel.
Click to expand...

TBH I've never even connected to iSCSI without MPIO installed. It's just added for any server i know I'm using with iSCSI, which is pretty much all of them for me. Good to hear you got it working though
 
oddjob62,
you seem to have experience of using iSCSI, how do you configure your NICs?

Jumbo frames = 9000
Set the Link speed to max, not Auto

also have you seen this http://support.microsoft.com/kb/2020559?

I also seen it suggested that you should also disable File and print sharing on the iSCSI NICs?

Any other settings I need to consider?
 
ASE001 said:
oddjob62,
you seem to have experience of using iSCSI, how do you configure your NICs?

Jumbo frames = 9000
Set the Link speed to max, not Auto

also have you seen this http://support.microsoft.com/kb/2020559?

I also seen it suggested that you should also disable File and print sharing on the iSCSI NICs?

Any other settings I need to consider?
Click to expand...

I've been advised on numerous occasions to leave 1gig NICs as auto
Yeah jumbo frames, remember to enable on the switch and the target as well.
Also on the switch disable unicast storm control, enable flow control, and disable spanning tree on iSCSI ports (assuming these exist).

There are quite a few issues that can arise from the various offload functions that modern NICs have (eg TCP Offload, VMQ), but this will depend on what NIC you are using, driver/firmware versions, etc (I've just spent quite a few hours fixing a slowness issue caused by mismatched VMQ configuration on my new 2012 cluster).

RE the link, are you planning on using passthough disks?
 
oddjob62 said:
RE the link, are you planning on using pass though disks?
Click to expand...

No it's a physical Active/Passive SQL cluster. That's why I'm keen to workout the optimal settings. I can't afford to have performance issues once it goes live, change control makes it painful to modify anything after that point!
 
ahh ok, well that link applies to hyper-v guests with lots of passthrough disks.

I would suggest talking to your server and SAN suppliers about recommended settings, ours for example only told us when we logged an issue with them that they recommended we do not use the iSCSI offload engine feature on their cards
 
oddjob62 said:
I would suggest talking to your server and SAN suppliers about recommended settings, ours for example only told us when we logged an issue with them that they recommended we do not use the iSCSI offload engine feature on their cards
Click to expand...

+1

I've been roped into setting up a Fujitsu Eternus iSCSI SAN and the technical doc's say to disable flow control which seems unusual.
 
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