alternate link limit

[Jeff Cai]

From the man page of vgextend command, it is said that the alternate link is limited to 7,
so Currently LVM supports a maximum of 8 paths to a physical volume (7 alternates and one primary).

Right now we have more than 7 alternate link to the same disk, is there any way to enlarge the limit(for example to 16)?

[James R. Ferguson]

Hi:

I don't believe that there is any provision for extending this limit. Perhaps, more interesting, is the question of "why". Remember, LVM alternate links (pvlinks) are for high-availability only. That is, the primary link (first in 'etc/lvmtab') performs the I/O whereas a secondary, tertiary, etc. becomes active only in the event the primary fails.

Regards!

...JRF...

[Uday_S_Ankolekar]

Yes, Seven is the limit for alternate links. I wonder why you need 7 alternate links?

USA..

[Ken Hubnik_2]

Uday
Why does a cat need 9 lives????

[Michael Steele_2]

This limitation is going to be HW specific to the server's and disk array's limitations via HBA's (* Host Bus Adapters *). Its not as easy as how many alternate PVlinks are allowed in LVM. There are redundantcy limitations.

[Michael Duthie]

Jeff,

At a guess I'd say you need to change that FC Hub for a couple of Brocades :-)

Mike

[Geoff Wild]

Well, if you need that much redundancy, if you are on an EMC - then I suggest you invest in EMC Powerpath - let that do the redundancy and load balencing at the back end for you.

Rgds...Geoff

[Michael Steele_2]

Redundancy!

[Dave Wherry]

To be redundant, I'll ask why?
One life is more than enough for a cat.