FROM AIX 5.3 INFOCENTER...


A kernel process (kproc), called an AIO server (AIOS), is in charge of each request from the time it is taken off the queue until it completes.

If the data that is being accessed asynchronously is located in a Journaled File System (JFS), all I/O is routed through the AIOS kprocs.

If the data that is being accessed asynchronously is located on a RAW logical volume management or the Enhanced Journaled File System (JFS2) in conjunction with concurrent I/O (CIO), the I/O is routed using a fast path and DOES NOT go through the AIOS kprocs. In that case the number of servers that are running is not relevant.

However, if you want to confirm that an application that uses raw logic volumes or JFS2 with CIO is taking advantage of AIO, you can disable the fast path option using System Management Interface Tool (SMIT).

[ 本帖最后由 unixnewbie 于 2008-7-24 09:43 编辑 ]

引用:

原帖由 unixnewbie 于 2008-7-23 08:57 发表
A kernel process (kproc), called an AIO server (AIOS), is in charge of each request from the time it is taken off the queue until it completes.

If the data that is being accessed asynchronously is located in a Journaled File System (JFS), all I/O is routed through the AIOS kprocs.

If the data that is being accessed asynchronously is located on a RAW logical volume management or the Enhanced Journaled File System (JFS2) in conjunction with concurrent I/O (CIO), the I/O is routed using a fast path and DOES NOT go through the AIOS kprocs. In that case the number of servers that are running is not relevant.

However, if you want to confirm that an application that uses raw logic volumes or JFS2 with CIO is taking advantage of AIO, you can disable the fast path option using System Management Interface Tool (SMIT).

agree

hahabean 和unixnewbie 说的都很好
得到相反的结论其实可以理解,这是一个系统问题也是一个数据库问题.有的是从系统方面理解有的是从数据库方面理解.
如果单纯从系统方面讲 AIX 800讲的很正确
对于DB2来说这个问题跟OS的类型和版本有关系.对于现在版本来说DB2一定会用到AIO的不管tablespace 是否是RAW.没有了系统的AIO,DB2仍然有许多自己的buffer需要AIO,不过此时不是由maxservers来控制.
大家可以尝试一下在AIX 5.3上把AIO禁用看一下结果

,DB2仍然有许多自己的buffer需要AIO ??能具体说说吗？我对这个不太清楚。

AIO with raw devices is not affected by whether DIO is on or off.

AIO with filesystems forks into two cases... buffered filesystems (DIO off), and unbuffered (DIO on).

AIO + DIO support (unbuffered filesystems) is built into many distribution kernels. Turning off DIO means AIO is also silently turned off.

AIO + buffered filesystem support (DIO off) may not be built into the distro kernel. There is no way to tell if it is supported except from the performance numbers.

那看来AIO 还是和raw devices 有关系的啊

For example,page cleaner,prefetch....

引用:

原帖由 我笨故我在 于 2008-7-23 11:38 发表
For example,page cleaner,prefetch....

possible

不管你是否使用raw，aio都是需要的
prefetch的能力应该和aio有关系

first get clear what OS you are talking about, second get clear what DB products you are concerned about.