Comments on: Fibre Channel to Software iSCSI Failover Failures

By: slowe

slowe — Mon, 18 Jul 2011 13:20:09 +0000

NiTRo, thanks for the follow-up. Last time I checked, though—and this might have changed—presenting the same LUN to the same host via two different protocols (which would be required in order to do the failover) isn’t supported by VMware. I’m not saying it doesn’t work, just that last time I checked it isn’t supported.

Nevertheless, thanks for the additional information and for the follow-up!

By: NiTRo

NiTRo — Mon, 18 Jul 2011 00:03:42 +0000

Hi guys, i know it’s an old post but as i was testing FC on Nexenta I gave a shot to try it and it actually works very well. Check out the video on my blog post http://www.hypervisor.fr/?p=3164

By: Spaceboy

Spaceboy — Thu, 29 Jan 2009 16:07:19 +0000

Yes, it works, even under IOMeter stress load.

But one must add the Disk TimeOutValue to Win registry to let them survive the failover delay. I’ve set it to 60 (seconds) and it works. While paths switch, IOs stall, but resume. WOW! (not the Vista kind

I’m wondering about setting some kind of path cost for iSCSI to force VMWare to fail back to FC if available – 4 GBit >> 1 Gbit. Any ideas?

By: slowe

slowe — Mon, 09 Jun 2008 20:23:04 +0000

Glenn,

Yes, that’s certainly possible, but what I was trying to achieve was having another layer of redundancy with what was already provided “out of the box,” so to speak. I plan to continue testing to see if there is any way to make this work.

I appreciate your comment. Thanks for reading!

By: Glenn Dekhayser

Glenn Dekhayser — Mon, 09 Jun 2008 16:46:04 +0000

Scott-

Just a theoretical here; what about putting in a FC-to-iSCSI bridge, so that you’re not failing over to a new stack? I think that would simplify this situation, by making the iSCSI path appear to exist in the FC world. Of course, you’d probably need to build an additional seperate fabric, which means additional FC card (ugh), but it would technically be supported right? Really expensive, but then again, we’re talking FC SANs!

-Glenn

By: Jon

Jon — Tue, 29 Apr 2008 10:59:11 +0000

I have seen this behaviour when a failover of two fiber paths. Even if the error looks to be in the ESX, you can try to change this registry entry (being a w2003):
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Disk\TimeOutValue
BTW, what do the event logs in the w2003 are saying?

If you can try with a linux VM you probably will see the root (/) partition going read only (for example Red Hat Linux 4 Update 4 needs this rpm http://kb.vmware.com/KB/51306 in order to prevent going on Read Only in the event of a fail over)

Hope this helps, congratulations for the blog!
Jon

By: william bishop

william bishop — Mon, 28 Apr 2008 22:52:21 +0000

Scott, what do the logs tell you from that timeframe?

By: slowe

slowe — Mon, 28 Apr 2008 19:24:33 +0000

Duncan,

I thought it worked, too, until I ran the tests with IOmeter. I’m going to keep trying, and I’ll let you know if I get any different results.

Nick,

It seemed to me like it should work, too. I was able to manually fail over the paths as long as IOmeter wasn’t running.

As for the DiskTimeOut value, I’ll try that, but the error really seems to be at the ESX level. The Windows VM just kept on chugging.

Thanks!

By: Duncan

Duncan — Mon, 28 Apr 2008 15:44:48 +0000

one of our trainers tested this a while back and he told me that it worked. but if he stressed it with iometer i doubt. will asks it tomorrow if I see him.

By: Nick Triantos

Nick Triantos — Mon, 28 Apr 2008 15:16:20 +0000

Theoretically, this config should work, although, it’s not supported by VMware and by extension the majority, if not all, storage vendors.

Although, it sounds like a good solution, customers tend to be leary using different stacks. In fact we’ve supported this type of config for standalone windows environments and some UNIX environments (i.e HP-UX) for sometime now.

Try setting the Disk TimeOutValue(default=10″) in the Windows registry to be higher than the FC HBA driver timeout. It’s quite possible the Disk Class driver’s timing out the requests prior to the path switch been completed, especially if you’re queuing a whole bunch of requests…which you are.