Amazon EBS Snapshot 如何确定修改的文件？
通常，同步应用程序根据文件大小更改和修改日期来检测文件修改。这对于 Amazon EBS 快照进程是否适用？
最近，我注意到一个固定大小的文件被排除在快照之外，即使该文件在一段时间内被修改了多次。当最新的快照（实际上是第一个快照之后创建的任何快照）加载到新实例时，只有初始内容可以位于文件中。甚至文件的修改日期也被设置为初始日期。
这让我想知道 Amazon EBS Snapshot 如何确定修改的文件。我可以更改任何配置以确保固定大小的文件正确添加到快照中吗？
Typically, a sync application detects file modifications based on file size changes and modified dates. Does this hold true for Amazon EBS Snapshot processes?
Recently I noticed a fixed sized file was excluded from a snapshot even though the file was modified numerous times over a period. When the most recent snapshot (in fact, any snapshots created after the first one) was loaded into a new instance, only the initial content could be located within the file. Even the modified date on the file was set to the initial date.
This made me wonder how Amazon EBS Snapshot determines modified files. Are there any configurations I can change to ensure fixed sized files are added to snapshots correctly?
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是的，但它是在块级别上执行的。也就是说，它检测更改的低级块而不是文件。
Yes, But it does so on a block level. That is, it detects changed low-level blocks rather than files.
EBS 确实使用块级差异来确定要存储的内容（如 @Dmitry 所说）。但是，EBS 还会保留所有以前存在的快照，以便将文件系统的状态完全重新创建为拍摄快照时的状态。
如果您的快照显示给定文件的旧状态，那么您肯定正在查看旧快照。
http://aws.amazon.com/ebs/
EBS does use block level diffs to determine what to store (as @Dmitry says). However, EBS also keeps all previously existing snapshots that are needed to fully re-create the state of the file system in the state it was in when the snapshot was taken.
If your snapshot shows an old state of a given file, you certainly are looking at an old snapshot.
http://aws.amazon.com/ebs/