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Old 07-09-2012, 01:01 AM
Alasdair G Kergon
 
Default DM MULTIPATH: Allow dm to send larger request if underlying device set to larger max_sectors value

Why is this separate from dm_set_device_limits?
Why is this not handled by blk-settings.c?
Should max_sectors be preserved across a table reload?

Alasdair

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Old 07-09-2012, 12:34 PM
"Chauhan, Vijay"
 
Default DM MULTIPATH: Allow dm to send larger request if underlying device set to larger max_sectors value

Hi Alasdair,

On July 09, 2012 6:32 AM, Alasdair Wrote:
>
>Why is this separate from dm_set_device_limits?
Ideally it should have been taken care in dm_set_device_limits but to find
minimum of max_sectors value among physical paths in dm_set_device_limits seems tricky.
I will look into it to use dm_set_device_limits.

>Why is this not handled by blk-settings.c?
blk_stack_limits do compare max_sectors between dm & physical path and minimum
between two values is then set to max_sectors of dm. But if underlying paths
are set with higher value, dm's max_sectors will be always set to default being
minimum. Rather objective is to set minimum of max_sectors among underlying paths but
not exceeding dm's max_hw_max_sectors

>Should max_sectors be preserved across a table reload?
Intentions is to set max_sectors to maximum capable when dm device is created. Even if
we reset max_sectors_kb from sysfs, restart of multipathd would again reset it to default.
Not sure if I answered your question.



Thanks,
Vijay

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