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Any way to tune pvlinks failover times?

 
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Geoff Wild
Honored Contributor

Any way to tune pvlinks failover times?

Want to know if there is a tuning option to decrease the time a primary path fails over to an alternate one.

Thanks....Geoff
Proverbs 3:5,6 Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make all your paths straight.
9 REPLIES 9
Dietmar Konermann
Honored Contributor
Solution

Re: Any way to tune pvlinks failover times?

Geoff,

it's the pv timeout that is responsible. Use pvchange -t to change it.

Best regards...
Dietmar.
"Logic is the beginning of wisdom; not the end." -- Spock (Star Trek VI: The Undiscovered Country)
Geoff Wild
Honored Contributor

Re: Any way to tune pvlinks failover times?

Cool - how do you know what the "driver default is"?

Set the IO_timeout value for a physical volume to zero (0) to use the
driver default:

pvchange -t 0 /dev/dsk/c2t0d2


-t IO_timeout Set IO_timeout for the physical volume to the
number of seconds indicated. An IO_timeout
value of zero (0) causes the system to use
the default value supplied by the device
driver associated with the physical device.
IO_timeout is used by the device driver to
determine how long to wait for disk
transactions to complete before concluding
that an IO request can not be completed (and
the device is offline or unavailable).


Thanks...Geoff
Proverbs 3:5,6 Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make all your paths straight.
Geoff Wild
Honored Contributor

Re: Any way to tune pvlinks failover times?

Also, do you know if there are any trade offs?

IE - If I set it to 1 second - will there be any issues?

Thanks...Geoff
Proverbs 3:5,6 Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make all your paths straight.
RAC_1
Honored Contributor

Re: Any way to tune pvlinks failover times?

If I remember correctly, the default is 60 secs.
Setting it to 1, would cause some problems like I/O timeout, SCSI resets. For example, If a write request could not be completed in 1 sec, it would result in I/O timeout. 1 sec would be too low. Go for the defaults.

With internal disks, I set it to default or 120 secs. For SAN disks, I set it to 120-180 secs.

Anil
There is no substitute to HARDWORK
Sundar_7
Honored Contributor

Re: Any way to tune pvlinks failover times?

Trade off is obvious. If the primary path has not failed but just too busy to respond or process the request then it will be switched to the secondary path.

This is OK as long as all of your primary paths have nt failed over to the secondary :-)
Learn What to do ,How to do and more importantly When to do ?
Sundar_7
Honored Contributor

Re: Any way to tune pvlinks failover times?

Default PV time out is 30 secs.
Learn What to do ,How to do and more importantly When to do ?
Geoff Wild
Honored Contributor

Re: Any way to tune pvlinks failover times?

AT our site - with EMC - just found out the default with HP on DMX's is 30 secs.

But here's what happens.

If a time out occurs (30 secs), LVM sends a test IO, then waits another 30 secs, then it fails over - and waits a further 15 seconds before allowing access to alternate link - total time: 75 seconds

On a time sensitive system that does transaction processing - it is way too long.

Rgds...Geoff
Proverbs 3:5,6 Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make all your paths straight.
Geoff Wild
Honored Contributor

Re: Any way to tune pvlinks failover times?

BTW - we have been testing Powerpath - but that is even worse for fail over times (at least on a DMX800).

Rgds...Geoff
Proverbs 3:5,6 Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make all your paths straight.
Dietmar Konermann
Honored Contributor

Re: Any way to tune pvlinks failover times?

Geoff,

your observations are correct. See also http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=430929. Default timout is indeed 30 secs.

Best regards...
Dietmar.
"Logic is the beginning of wisdom; not the end." -- Spock (Star Trek VI: The Undiscovered Country)