The fourth line cleans up the index. IndexWriter physically deletes from the disk the documents that have been marked as deleted.
第4行对索引进行清理，清理过程中将把所有标记为删除的文档物理删除。
2
Once the disk has passed all of these tests, the disk resource is marked as online and the cluster service then continues to bring all other resources online.
当磁盘通过所偶的测试后，磁盘资源被标记为上线，集群服务继续上线其他资源。
3
Because ZFS never overwrites data but instead writes to a new location, older data can be preserved (but in the nominal case is marked for removal to converse disk space).