LVM and PV Timeouts

[Paul_20]

I am trying to get an understanding on how LVM and PV work together. If I have a disk w/ alternate PV links and it's PV timeout values are left to it's default value (60) and LVM timeout is left at it's default value (60) How are the alternate links ever used? My understanding is that if LVM and PV Timeouts are set to the same 60 second intervals that would never allow time to switch to the alternate PV link? Is that a correct assumption?

Thanks

[Alan Riggs]

Alternat links are generally used to provide a redundant access in the event of controller failure. It is designed to eliminate single points of failure, not provide load ballancing.

Often, when alternate links are used an SA will also alternate the defined primary, thus splitting the load on the individual SCSI channels.

[Byron Myers]

I believe the default LVM timeout is forever. If the LVM and PV link timeouts were indeed the same, then I agree with you that a PV swithchover would not complete.

[Paul_20]

Just to be make sure I understand ... If PV and LVM timeouts are left to their defaults ... you do have a single point of failure because if the primary path fails, LVM will continously attempt to connect to the primary path w/o attempting to failover to the alternate?

[James A. Donovan · Accepted solution]

Speaking as someone who has never modified the default timeouts for those parameters, I can tell you that by using the defaults, if you lose one path to the device the alternate link WILL kick in and let you continue processing.