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对于11.2之前的版本，很多环境的重启原因（top5的情况）是由于NTP调整时间的步伐过大导致的，所以RAC环境中，我们建议用户如果使用NTP，需要配置成微调模式；
如何诊断节点重启问题
这里介绍几个主流linux和unix平台上NTP微调的配置方法：
For Linux ：
1.请确确认各节点的ntp包已经安装 ,我这里是个4.2.2的版本
[oracle@nascds10 ~]$ rpm -qa | grep ntp
ntp-4.2.2p1-9.el5_4.1
2.请编辑各个节点的ntp.conf文件
[oracle@nascds10 ~]$ su - root
Password:
[root@nascds10 ~]# vi /etc/ntp.conf
#New ntp server added by Robinson
server 192.168.1.128 prefer <<<<===========这里是时钟服务器
restrict 192.168.7.0 mask 255.255.255.255 nomodify notrap #基于网段的限制（限制在网段192.168.7.0）
broadcastdelay 0.008
[root@nascds11 ~]# vi /etc/ntp.conf
#New ntp server added by Robinson
server 192.168.7.71 prefer
broadcastdelay 0.008
3、配置ntpd的参数，我们主要强调的是要配置成"微调的模式" 也就是在options中要加入 -x的选项
[root@nascds10 ~]# vi /etc/sysconfig/ntpd
#The following item added by Robinson
#Set to 'yes' to sycn hw clock after successful ntpdate
SYNC_HWCLOCK=yes
OPTIONS="-x -u ntp:ntp -p /var/run/ntpd.pid"
[root@nascds11 ~]# vi /etc/sysconfig/ntpd
The following item added by Robinson
SYNC_HWCLOCK=yes
OPTIONS="-x -u ntp:ntp -p /var/run/ntpd.pid"
4、自动启动配置
[root@nascds10 ~]# chkconfig ntpd on
[root@nascds11 ~]# chkconfig ntpd on
5、重启一下，使最新配置生效
[root@nascds10 ~]# service ntpd restart
Shutting down ntpd: [ OK ]
ntpd: Synchronizing with time server: [ OK ]
Syncing hardware clock to system time [ OK ]
Starting ntpd: [ OK ]
[root@nascds11 ~]# service ntpd restart
Shutting down ntpd: [ OK ]
ntpd: Synchronizing with time server: [ OK ]
Syncing hardware clock to system time [ OK ]
Starting ntpd: [ OK ]
6、检查ntpd进程的状态
[root@nascds10 ~]# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
LOCAL(0) .LOCL. 10 l 40 64 1 0.000 0.000 0.001
[root@nascds11 ~]# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
test.oracle.com .INIT. 16 u 60 64 0 0.000 0.000 0.000
LOCAL(0) .LOCL. 10 l 59 64 1 0.000 0.000 0.001
For Aix:
1. NTP的同步设置 编辑 /etc/ntp.conf文件, 内容如下:
----------------------------
#broadcastclient
server 192.168.5.2
driftfile /etc/ntp.drift
tracefile /etc/ntp.trace
slewalways yes
----------------------------
我们这里还是要强调微调slewalways ,这个值的默认设置是no，也就是说如果您不设置，NTP大可一次调整1000秒. 根据IBM的官方说明，如果我们不指定slewthreshold 那么默认值是 0.128 seconds. 如果想特别设置，请指定slewthreshold 的值，注意单位是second
2.在NTP客户端启动xntpd守护进程
# startsrc -s xntpd
3. 查询xntpd的状态
当 system peer 不为 'insane' 时, 表明客户端已与服务器端成功地进行了同步.
# lssrc -ls xntpd
Program name: --/usr/sbin/xntpd
Version: -------3
Leap indicator: 00 (No leap second today.) Sys peer: ------192.168.5.2 ...
关于更多的关于IBM的平台上NTP的设置，可以参考IBM的官方文档解释：
http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.files/doc/aixfiles/ntp.conf.htm
For HP UX:
NTP在HP上的配置，是比较省心的，不容易导致RAC重启的，因为HP上的NTP默认的就是微调的模式
1、首先我们还是要编辑ntp的配置文件 /etc/rc.config.d/netdaemons，把 XNTPD 设定为1表示启动
export XNTPD=1
2、编辑配置文件 /etc/ntp.conf ，配置好时间同步服务器
server 192.168.5.2 # 第一个地址是主服务器
server 192.168.5.3 # 第二个地址是备用服务器
3、启动ntp的进程
# /sbin/init.d/xntpd start
4、检查NTP的状态
# /usr/sbin/ntpq -p
这个命令您会看到同步的地址
如果出现的结果是No association ID's returned 那么表示您失败了
关于HP主机上NTP的模式，有3种如下，在HP 平台的man page中有详细的说明：
模式1：offset below 128 milliseconds
This is the normal operating regime of NTP. A properly configured NTP hierarchy (with reasonable networking) can operate for years without ever approaching the 128 millisecond upper limit. All time adjustments are small and smooth (known as slewing), and nobody even notices the slew adjustments unless they have a cesium clock or a GPS clock and expensive instrumentation to make sophisticated measurements (HP/Agilent makes the instruments).
模式2：offset above 128 milliseconds
This regime is often encountered at power-on because, those battery-backed real-time clocks they put in computers are not too great. Because NTP is quite capable of keeping the offset below one millisecond all the time it is running, many users want to get into the normal regime quickly when an offset above 128 millisecond is encountered at startup. So in this situation NTP will (fairly quickly) make a single step change, and is usually successful in getting the offset well below 128 millisecond so there will be no more of the disruptive step changes.
模式3：offset above 1000 seconds
This is so far out of the normal operating range that NTP decides something is terribly wrong and human intervention is required. The daemon shuts down.
For Solars:
我这没有测试的平台，不过在KM (How to Configure NTP or Windows Time for Oracle Clusterware (Doc ID 1056693.1))里找到了配置的办法，这里还有Windows的配置方式
检查配置:
/usr/bin/svcs ntp
STATE STIME FMRI
online 7:39:29 svc:/network/ntp:default
ps -ef|grep ntp
root 21212 1 0 Feb 02 ? 0:33 /usr/lib/inet/xntpd
配置/etc/inet/ntp.conf 启用slewalaways
grep 'slewalways|pll' /etc/inet/ntp.conf
slewalways yes
disable pll
启动:
/usr/sbin/svcadm enable ntp
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