最近新部署Exchange 2019，虽然变化不大，但是也遇到了一些小问题。随着深入研究，就能发现一些以前被忽视的点。
Exchange完成备份后，数据库日志并没有被清除，依然存在。https://blog.csdn.net/qishine/article/details/106500912
可以看到备份完成后，之前的日志依然存在。检查备份软件，发现备份成功。检查Exchange日志2046
Database log truncation has been requested for this database. Log truncation will occur on the active copy after the next log generation is created. Log truncation will occur automatically on the passive copies after that log file is copied.
可以看到，Exchange也知道备份成功了，可以清除日志了。但是日志确实还在啊。
最后找到了微软的文章。
https://docs.microsoft.com/en-us/Exchange/high-availability/ha-changes?view=exchserver-2019
In Exchange 2013 or later, the system is able to provide fast failover while using a high checkpoint depth on the passive copy (100 MB). Because passive copies have 100-MB checkpoint depth, they've been de-tuned to no longer be so aggressive. As a result of increasing the checkpoint depth and de-tuning the aggressive pre-reads, IOPS for a passive copy is about 50 percent of the active copy IOPS.
后期的Exchange为了提供更快的故障转移会保留100M的日志。所以，我们这个问题也得以解释了，为什么备份成功后日志依然存在。
文章中图片使用的检查脚本可以在这里下载，其中有针对Exchange 2019的特别修改，确保能够运行。
Test-ExchangeServerHealth.ps1
https://download.csdn.net/download/qishine/12489589
Get-ExchangeEnvironmentReport.ps1
https://download.csdn.net/download/qishine/12489583