Re: md multipathing failover

[Ed Wilts <ewilts ewilts org>]

On Fri, Apr 22, 2005 at 06:02:22PM +0200, Gunther Schlegel wrote:
> I am becoming a little desperate with my SAN (EMC Clariion, Qlogic HBAs)
> connections.
> 
> With RHEL3 I just use the internal failover of the Qlogic driver. This
> works fine. 
> 
> However, the Qlogic-modules in FC2, FC3 and RHEL4 lack this feature.

It works fine with my HP EVA storage in RHEL3.

> These FC2/3 hosts should be upgraded to RHEL4 quite soon. As the
> failover is 
> missing I tried to convert the SAN-attached filesystems to md
> multipathing. 
> 
> In general it works fine, but I tested the failover on a FC2 host
> (latest errata kernel). The result is that the md0_multipath thread
> takes up all the CPU ressources but does not actually switch to the
> alternate path.
> 
> Besides, the multipath device is not assembled in a correct way during
> bootup on FC2 as it uses raidtools instead of mdadm, but I corrected
> this at runtime, so this cannot be the reason.
> 
> Question: - Does multipathing actually work with RHEL4? 

>From everything I've read on the nahant list, it does not.  Please
search the archives - you'll find a lot of interesting threads.

> Does it work on RHEL3? Does it even work on FC2 and
> I am just missing something?

As I said above, it works fine for me with HP EVA storage and the qlogic
driver out of the box.  I hammered it hard with bonnie++ while turning
switch ports on and off and it behaved exactly as it should.
 
> Sorry for crossposting and referring to Fedora Core, but I hope some
> RHEL admins also run Fedora. The guys on the Fedora lists do not seem to
> deal with stuff like SANs.

It doesn't make much sense to me to run Fedora on a SAN...

-- 
Ed Wilts, RHCE
Mounds View, MN, USA
mailto:ewilts ewilts org
Member #1, Red Hat Community Ambassador Program