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Async. I/O problems.

Vijay Ravula
Occasional Visitor

Async. I/O problems.

We have HP 9000 system with two processers and 1GB of physical memory.
And sybase is configuerd to use async. i/o device and configures with 224 MB of memory.

When I try to increase memory of sybase, system brings up the devices in standard i/o rather than async. i/o.
If I set the memory back to 224 again..and bounce the system...sybase comes up with async. i/o.

I think there's something on HP side which is stopping me from using both.
Could someone help me on this.

shmmax is set to 1GB.

4 REPLIES
Philip Chan_1
Respected Contributor

Re: Async. I/O problems.

Hi,

Another governing factor is the "shmmax" kernel parameter. You must set it high enough for increasing the amount of physical memory Sybase could grab. The shmmax value should set to a value that is larger than the amount of memory your server have got.

Another chance for not being able to start async I/O is that there weren't enough lockable memory because other processes were holding up the memory. In such cases, reboot your server and make sure Sybase is the first application to start.

Rgds,
Philip
Vijay Ravula
Occasional Visitor

Re: Async. I/O problems.

Thanks for the reply.
To my knowledge shmmax should be equal to physical memory and it is set to 1GB in the system.
I have 63 devices in sybase for async i/o mode.
Is more number of devices configures causing the problem..or any other way of increasing memory for sybase as well as making use of async i/o for all 63 devices.

Thanks,

Vijay


Re: Async. I/O problems.

There should be some general guidelines about several hp-ux parameters and their settings in the Sybase installation guide. I don't remember all of them off of the top of my head -- it may be shmmax that's gating you, or it may be something else.

In any case, in general when Sybase is unable to get as much memory as it would like to get, starting devices with standard I/O instead of async I/O is a pretty common sympton that happens as a result.
Philip Chan_1
Respected Contributor

Re: Async. I/O problems.

Vijay,

Have you granted the sybase user the MLOCK right? see "man 1m setprivgrp" for details.

You can try creating the file /etc/privgroup which contain one single line text as

sybase RTPRIO MLOCK CHOWN

reboot server for that to take effect then try starting dataserver again and see.

Rgds,
Philip