hp-ux num_tachyon_adapters kernel parameter

[Fred Ruffet]

hi,

What is the purpose of this parameter : num_tachyon_adapters. What is the problem if it is set to 0 when having a tachyon card ? What can it cause if set to more or less than the real number of tachyon adapters ?

Regards,

Fred

[B. Hulst]

Hi,

This seems to be limited nowadays to max 5.
Maybe it allocates too much memory per adapter.

Regards,
Bob

[Fred Ruffet]

My main problem here, is that I have 2 servers with tachyon cards (one each). One has this parameter set to 5, the other one to 0. And I don't know if it can cause troubles.

Regards,

Fred

[B. Hulst]

Hi,

The (common sense or real) limit seems to be anyway set to 5.

Most software that change kernel parameters at installation time set this to either 1 or 2.
If you have the adapters or not. :)

For your system with 0 I would set it to 1.

And if, you want to keep your systems in similar configuration then the other one could go from 5 to 1...since there is only one adapter in each machine.

Regards,
Bob

[Fred Ruffet]

Thanks for the advice. I understand it must be set to 1 on both servers, and I planned to do it (requires reboot), but I'm still interressed in knowing what problems may occur with bad settings...

Regards,

Fred

[David Child_1 · Accepted solution]

Fred,

If memory serves the only drawback to setting this parm too high is you will waste resources (the system will use up a certain amount of memory for each one). If set to '0' I believe it will work, but will not set up the memory buffers and therefore may not perform as well.

Also, I am fairly sure this parm only applies to Tachyon cards, not the newer Techlite cards.

David

[David Child_1]

Fred,

Here is some additional details (clarifications). No need for points on this one.

num_tachyon_adapters specifies how many Tachyon FCP adapters are installed in the system so that an appropriate amount of memory can be allocated for them at system start-up ***if the system does not provide I/O virtual addressing***.

If your system does not provide I/0 virtual addressing, set num_tachyon_adapters equal to the number of Tachyon FCP adapters actually installed in the machine. During boot-up, the system then reserves a corresponding amount of memory for use by those adapters, varying that amount according to the value of max_fcp_reqs.

If the system supports I/O virtual addressing, set this parameter to zero. The system then automatically allocates memory as needed.

If you do not know whether your system provides I/O virtual addressing, setting this parameter to a non-zero value is harmless, provided the value does not exceed the number of Tachyon FCP adapters actually installed in the system. If the value exceeds the number of installed adapters, a corresponding amount of memory is wasted because it cannot be used for other purposes.

David

[Fred Ruffet]

Thanks for this explanation David.
I had it set to 0 on one machine and this one was having performance problems. I set it to 1, but it doesn't seem to be really better...

Thanks again,

Fred