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30 second delay for iSCSO MPIO SAN access after disconnected NIC

30 second delay for iSCSO MPIO SAN access after disconnected NIC

jeudi 15 avril 2010 15:41

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   I am using Windows 2008 R2 servers to connect to an HP MSA2312i iSCSI dual-controller SAN using the Microsoft DSM MPIO driver. I have two connections configured in the iSCSI Favorite Targets and the MPIO load balance policy is set to "Round Robin With Subset". The problem is that when I test unplugging a NIC card (or power down one of the two switches) it seems to take up to 30 seconds for the server to allow access to the SAN. (I'm just doing a simple test using Explorer to see if I can create folders on the iSCSI volume).
   Is this down time normal? Is this a configuration problem on the Windows side? I tried changing the Microsoft DSM settings in Disk Management - Disk - Properties - MPIO - DSM Details to:
Path Verify Period: 5
Path Verify Enabled: checked
PDO Remove Period: 4
   I don't know if these changes were necessary, but even with these changes, I still have the slow connection time after a NIC/Switch disconnection.
   If anyone has any insight into this, it would certainly be greatly appreciated! :-)
dave

Toutes les réponses

samedi 17 avril 2010 02:49

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Hi Dbaddorf

what happens if you use auto failover policy in MPIO settings. do you get same delay then too?

Gaurav Anand
samedi 17 avril 2010 02:49

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Hi Dbaddorf

what happens if you use auto failover policy in MPIO settings. do you get same delay then too?

Gaurav Anand
lundi 19 avril 2010 15:44

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Gaurav,

Thanks for your response. When I use the "fail over only" policy in MPIO (instead of the Round Robin policies) I see the same amount of time to regain connectivity to the SAN storage.

thanks.. dbaddorf
mardi 20 avril 2010 07:36

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Hi Dbaddorf

sorry for asking - but what happens when you use hp dsm software for iscsi based MSA. do you see same behaviour. Do you see anything in event logs. if not a netmon trace may be an option.

make sure you are not using multiple connections per session[MCS] along with MPIO.
Gaurav Anand
mardi 20 avril 2010 12:10

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Guarav,

   No problem for asking - I appreciate your help.

   Although I didn't get too much really good information from HP they did say that I shouldn't use any DSM from HP. In fact, I couldn't find any DSM for Windows 2008 R2 on their website.

   That's interesting that you brought up MCS - no I haven't configured it. I didn't see anything about setting up MCS in the HP documentation. From what I understand in Microsoft's iSCSI user's guide (http://download.microsoft.com/download/a/e/9/ae91dea1-66d9-417c-ade4-92d824b871af/uguide.doc), it seems that I should only use either MPIO or MCS, but not both:

Configure additional Paths for High Availability; use either Microsoft MPIO or MCS (multiple connections per session) with additional NICs in the server to create additional connections to the iSCSI storage array through redundant Ethernet switch fabrics.

Although it is technically possible to layer Microsoft MPIO and MCS together since they function at different layers in the Windows stack, Microsoft does not support the layering of MPIO and MCS due to complexities this can introduce if troubleshooting is needed on a configuration.

   I do see configuration guides from HP which recommend the MPIO configuration in Windows, so I'm assuming (from the above Microsoft quote) that I shouldn't also configure MCS. (I'm not even sure if it's supported on the HP MSA2312i).

Thanks... dave
dimanche 25 avril 2010 06:17

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Hi Dbaddorf

Also I understand that creating a folder from explorer may not be right test..you should check disk availability in device manager or disk management.msc

delay in creating a folder might be a performance issue and not connectivity issue.
Gaurav Anand
- Proposé comme réponse Gaurav.Anand itinfras.blogspot.com dimanche 25 avril 2010 06:17
lundi 26 avril 2010 12:02

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Guarav,

Thanks for your response. Although I questioned myself in my methodology for testing the availability of the storage through Windows Explorer, it seemed to be a valid test in that I could create folders instantly when the SAN was fully connected and when it had recovered after a failure of a single MPIO path. But the 20-30 seconds (or so) directly after a disconnection of one of the NIC's would cause Explorer to be in a state of "not responding". At the end of the 30 seconds, Explorer would respond again and the folder would be created.

I guess I'm not sure what the advantage is of looking at device manager or disk management to see what they report if I can't actually use the SAN for reading/writing during the recovery time. In other words, even if those tools say that the disks are available, if I can't access the disks it doesn't seem to help me. And if they report that the disk are unavailable, I know that they recover - I'm just wondering if the recovery time is normal or whether there is something that I can do to make it recover faster...

Thanks.. dave
mardi 27 avril 2010 06:38

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Hi Dbaddorf

Looking in disk manager and diskmgmt.msc helps in scoping down the issue. If the disks are not available in device manager means that OS just cant see them at that time..but if they are and we get delay...we are restricting the scope of the issue to Host OS. Also in such a scenario a netmon trace may help you during reproduction of scenario. I will suggest to ask HP support can they reproduce the issue in their environment on same storage and what results do they get!

sorry for not able to help you much in this regard other than generic suggesion
Gaurav Anand
- Marqué comme réponse dbaddorf mardi 27 avril 2010 11:51
mardi 27 avril 2010 11:51

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Gaurav,

Thanks for your help. I have gone to HP and they haven't been much assistance.

dave
mercredi 12 mai 2010 17:03

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How many shares are on the drive you are failing over? I have seen this same situation with clustered when there are many shared folders.
mercredi 12 mai 2010 18:11

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MDRTech,

I was doing the test with a single iSCSI volume and just a few folders on the NTFS filesystem.

Dave
mercredi 9 juin 2010 19:48

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Hi,

Apologies for the tangential question, but having read all of the above, is it possible to have a Windows 2008 HA arrangement that accesses and ISCSI SAN using just Multiple Connections per Session (MCS) - WITHOUT having MPIO enabled (as they appear incompatible).

This would allow me to have multiple NIC cards in each W2k8 node for the purposes of NIC failure and 'bandwidth' through multiple NICS.

I would have only one ISCSI session for W2K8 node - but that’s something I can live with.

I ask the question because I haven’t seen an explicit mention of W2K8 HA with MCS

Kind Regards

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