Asynchronous I/O Support On Windows (Doc ID 1228845.1)

rongshiyuan發表於2014-03-27

In this Document

Applies to:

Oracle Database - Enterprise Edition - Version 10.1.0.2 to 11.2.0.2 [Release 10.1 to 11.2]
Microsoft Windows Itanium (64-bit)
Microsoft Windows x64 (64-bit)
Generic Windows

Purpose

This FAQ document identifies the most frequently asked how-to questions regarding Asynchronous I/O in Windows environment.

Questions and Answers

1) Is Asynchronous I/O supported on Windows environment?

Microsoft Windows x64, Windows NT and Windows 2000 support Asynchronous I/O.

2) Documentation says DISK_ASYNCH_IO only affects "raw" filesystems. We have standard EMC filesystems.
Does this mean we are not taking advantage of asynchronous I/O at the disk subsystem level with DISK_ASYNCH_IO init parameter set to TRUE ?

DISK_ASYNCH_IO on Windows ports should retained at the default value of TRUE. Asynchronous I/O is enabled by default in the OS.

3) Filesystem DOES support asynchronous I/O - and we know we have DISK_ASYNCH_IO set to TRUE and FILESYSTEMIO_OPTIONS is unset (set to nothing currently) - are we currently leveraging asynchronous I/O to our datafiles? Most documentation says asynchronous I/O is not enabled until FILESYSTEMIO_OPTION is set to ASYNC or SETALL. In other words, do we need to set FILESYSTEMIO_OPTIONS to SETALL or ASYNCH before we achieve asynchronous I/O on our system?

No it does not need to be set. Asynchronous I/O is enabled by default at the OS.

4) With SAN filesytems setup for Async I/O and DISK_ASYNCH_IO=TRUE and FILESYSTEMIO_OPTIONS set to nothing, is there any other setting/configuration change required?

From Disk manager on SAN / NAS or other storage devices ensure you have Disabled Write Disk Caching on the disk, as the OS can not ensure the write makes it to disk on crash

5) If 'WRITE CACHE' option is enabled for all the LUNs, but not at the physical disk, should the 'WRITE CACHE' at the LUN level be turned off?

The problem with WRITE CACHE enabled is Oracle can not be held responsible in recovery situations as Oracle cannot ensure data actually made it to disk.

The WRITE CACHE will provide an ACK that the request has been received and and acknowledged as being complete while it could be held in CACHE.

So, Yes disable the Write Cache on the LUN's.

There is no problem with enabling Write Cache for normal DB operations except in the case of heavy writes and during a crash.