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应该是跟文件包含的块的分布有关系,按照官方文档的说法,指定section size后,每个备份片包含了一个file section,file section的指的是文件中连续的数据块,根据官网文档的说法,你的备份结果就比较合理了,有可能你的文件碎片比较多。
以下是官方文档:
If you specify the SECTION SIZE parameter on the BACKUP command, then RMAN produces a multisection backup. This is a backup of a single large file, produced by multiple channels in parallel, each of which produces one backup piece. Each backup piece contains one file section of the file being backed up.
file section
A contiguous range of blocks in a datafile. A multisection backup processes a large file in parallel by copying each section to a separate backup piece. |
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