Qlogic Failover/Loadbalancing

[Joe_P]

Hi All,

I would like to ask for some advice on HBA failover and loadbalancing settings.

Setup:

Redhat Linux 4.4 ia64
Redhat Linux 4.5 x86_64
Redhat Linux 4.4 x86
Qlogic dual channel HBA's.
EVA4100

These seem to be the default Qlogic HBA settings when using the ./INSTALL -f option:
ql2xfailover: default = enabled
ql2xlbType: default = static load balancing

How do these settings relate to the EVA Vdisk preferred path settings?

Apparently if you configure 'failover enabled' in the Qlogic driver, you have to present the Vdisk using either Path A Failover or Path B failover, and not use the 'Failback' option.

Also, according to the manual, Vdisk ownership will be transferred to the other controller if 60% of I/O requests will come through the non-owning controller.

Doesn't this conflict with the 'static load balancing' option in the Qlogic driver?
You need to present the Vdisk Path A Failover or Path B Failover because of the 'enabled' failover in the Qlogic driver, but because 'static load balancing'
is switched on, EVA might eventually switch ownership to the other controller?

I'm not sure how this works yet, but these are the settings I would like to go with:

ql2xfailover: enabled
ql2xlbType: static load balancing
Present Vdisks equally using Path A Failover and Path B Failover (or is 'no preference' still allowed when failover is enabled in the Qlogic driver?).

Does this make sense?

Thanks for your input.

[IBaltay]

Hi,

LVM2

maybe the LVM2 conceipt could be considered too:
http://www.guug.de/lokal/rhein-main/2004-09-23/LVM2_sage_23.09.pdf

Qlogic Linux forum:
http://solutions.qlogic.com/KanisaSupportSite/relateditems/forumleaf.do?TaxoName=FB_ForumBrowse&NodeId=FB_HBA_LINUX_1_2&NodeName=Fibre%20Channel%20Linux

http://solutions.qlogic.com/KanisaSupportSite/forum/viewthread.do?command=FRShowThread&threadId=Post-26646015&frStartInd=12&NodeId=FB_HBA_LINUX_1_2&NodeName=Fibre+Channel+Linux&TaxoName=FB_ForumBrowse

HP Qlogic approved
http://driverdownloads.qlogic.com/QLogicDriverDownloads_UI/Product_detail.aspx?oemid=21

Resume
if there is no ALB in the RedHat 4.x qlogic driver, then the EVA controllers need to be always balanced via the set preferred path....

[Uwe Zessin]

The EVA preferred path setting for a virtual disk is just a hint which countroller should own the virtual disk.

In the past, a host could overwrite the hint and force a failover, even on an active/passive array.


According to the user guide, you can use Path A/B failover or no preference, in which case the EVA will do round-robin ownership.


Now, the question is whether the QLogic driver understands asymmetric active/active access which the EVA does provide. In the worst case, all servers use the first path they can find. In that case, after some time, all virtual disks can end up being owned by one controller. I've seen somthing similar in a Windows environment.

It's been some time since I worked with the Linux drivers, so I can't help much, sorry.
I would try to find out whether the driver supports A/A/A to prefer its I/O to a path through an owned controller. Or how to configure static paths so that you can match the Linux path selection with the virtual disk preferred path settings (that should avoid any ownership transfers after the system is running for some time).