关于硬盘测试的结果

landi

用第一条命令测吧，不会有人在Web server上开dsync吧？

liheyuan

首先这个只能代表连续存储。
然后帮大家G了一下：
dsync是同步I/O，相对于异步来说会慢。

liheyuan

理解基本是正确的，先来原文：
For devices initialized on UNIX operating system files, the dsync setting controls whether or not writes to those files are buffered. When the dsync setting is on, Adaptive Server opens a database device file using the UNIX dsync flag. The dsync flag ensures that writes to the device file occur directly on the physical storage media, and Adaptive Server can recover data on the device in the event of a system failure.

When dsync is off (false), writes to the device file may be buffered by the UNIX file system, and the recovery of data on the device cannot be ensured. Turn off dsync only when data integrity is not required, or when the System Administrator requires performance and behavior similar to earlier Adaptive Server versions.

generally dsync is set to off for tempdb devices which is not required during recovery.

Note:The dsync setting is ignored for devices initialized on raw partitions, and for devices initialized on Windows files. In both cases, writes to the database device take place directly to the physical media.

liheyuan

对于Unix操作系统的文件来说，dsync控制被写入的文件是否被缓存（buffered）。如果dsync打开，打开数据库的连接可以使用dsync 标记。dstnc标记（打开）确保写入设备的文件直接被写入物理设备（而不经过buffer，以保证同步），XXXX。
如果dsync关闭，写入文件将会被buffer。恢复的数据可能不可信（因为可能断电时候部分在buffer里）。仅当数据集成不重要，或者系统需要高性能的时候，才建议关闭dsync。

概括：加dsync就不使用缓存了，是个测试测试I/O的好参数。