importance of fs_async and aio parameters

[jok]

Any idea of this kernel parameters;
BTW; I already have browse hp docs on kernel parameters but I can not find answer on this questions.

"fs_async", is this parameter applicable for RAW or is it only for unix filesystems.

"aio_*", As far as I know there is a minimum and maximum value for this, but my question is: Is there a tool that will let you know that this parameter is reaching its maximum or something like reaching its threshold.

thanks,

jok

[Philip Chan_1]

The kernel param fs_async only affects the asyn I/O on file systems. The driver file /dev/async is the one responsible for raw partition async I/O.

Async I/O is VERY important for database systems such as Oracle and Sybase. Without it these server processes would became single threaded because of the blocking reads/writes.

~Philip

[Pedro Sousa]

HI!
From the SAM's kernel parameter's help:
fs_async specifies whether or not asychronous writing of file-system data structures to disk is allowed. If no value for fs_async is specified, synchronous writes are used.
Synchronous writes to disk make it easier to restore file system integrity if a system crash occurs while file system data structures are being updated on the file system.
If asynchronous writes are selected, HP-UX file system semantics for NFS cluster environments are preserved. In addition, files opened using open() with the 0_SYNC flag (synchronous writing) will continue to be written synchronously when the asynchronous-writes feature has been configured into the kernel.
Asynchronous writes to disk can improve file system performance significantly. However, asynchronous writes can leave file system data structures in an inconsistent state in the event of a system crash.

for aio_*:
http://docs.hp.com/cgi-bin/fsearch/framedisplay?top=/hpux/onlinedocs/B2355-90684/B2355-90684_top.html&con=/hpux/onlinedocs/B2355-90684/00/00/7-con.html&toc=/hpux/onlinedocs/B2355-90684/00/00/7-toc.html&searchterms=aio&queryid=20010406-045520
good luck.