automatic failover of HBA with RHEL

[Dave Bruce_2]

We would like to connect a dual HBA RHEL server to an XP512. From what I can see the Red Hat volume manager does not provide automatic failover to the second HBA if the primary HBA fails like LVM does. Am I right? Do I have to look to Veritas' Storage Foundation for a solution? Are there other options?

[Ivan Ferreira]

I know that there are modules for the HBA that handles the failover. Also, secure path is available.

See:

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=959762

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=939917&admit=-682735245+1129923080175+28353475

[Slawomir Gora]

Hi,
if you use qlogic FC adapter, failover is build in qlogic driver for linux.

[Axel Thimm]

What RHEL version are you using? If it's RHEL4 then with Update 2 you get multipath support, which brings path failover and load balancing.

It is also independent of the HBA hardware you are using, i.e. works with qla and emulex the same.

For using qla's built in failover you need to build the driver yourself. The one that is shipping with RHEL4 doesn't have the failover and /proc/scsi support. But there are 3rd party packaged qla drivers for RHEL4 with failover support at

http://atrpms.net/name/qla2xxx/

[Steven E. Protter]

You handle this with the HBA configuration. If its qlogic, qlogic configuration handles failover.

SEP

[Ian Derringer]

So, if I use the codes from Qlogic controller, I do not need to use SecurePath? Does anyone here using SP with Linux RHAS 3.0? I heard from one person that SP running on RHAS 3.0 had a lot of failover issues, is this true??

I am in the process to either install SP 3.0C or using the codes that came with the Qlogic controllers. Please share your opinions on either method.

Thank you in advance.

Ian

[jleon]

Axel or Anyone,

I am about to deploy RHEL4 Update2 (32 bits)on a 4 Dual-core Opteron, connected to EMC DMX disk storage( 4 devices assigned to the host) using 2 Qlogic QLA2340 (each HBA has one path to each of the 4 devices).

Can you give me some details on how to setup device multipath, automatic failover/load-balance of the HBAs.

I am used to do it in HPUX and Solaris, but no experience in RHEL4. Usually we use powerpath in HPUX and Solaris, but if RHEL4 Update2 has the funtionalities build-in then we can save money if it works and performance is good.

Thank you very much in advance.

[Axel Thimm]

jleon,

first of all why use 32 bits version of RHEL4U2 on a 64 bits system?

Setting up multipath has become really easy with RHEL4U2:

- Comment the first three lines of /etc/multipath.conf to activate multipath, these are the definition of devnode_blacklist that blacklists everything at the beginning.

- chkconfig multipathd on and service multipathd start to have the multipath daemon running.

Now you can either reboot or use multipath -v2 to create your multipath devices. These devices are then called /dev/dm-, check with dmsetup ls. I suggest putting LVM on top of it, so you have persistent naming, e.g. something like /dev/mapper/storage-accounting etc.

[jleon]

Axel,


First of all thanks for the quick reply.

I will be using the 32 bits version of RHEL4U2 because one of our application does not support the 64 bits version.

Given that we are a HPUX shop, we surely will use LVM (HPUX people do not know any other way).

RHEL4's multipath, would that take care of HBA failover. How is the performance of load balance?

I have search google and not docs about RHEL4 multipathing. Do you have any documentation that I could have?

Thanks,
Juan L.

[Axel Thimm]

Juan,

I'm not aware of any Red Hat documentation update regarding multipath.

Are you sure that the x86_64 version of RHEL will not be able to run your 32 bit application? That's what it's been designed for (keyword is "multilib").

Performance of multipath depends on the SAN device used. Switching between qla's failover model and dm's multipath is easy, so you can benchmark your setup and decide on which method to use.