在SQL Server 2012（11.0.7001.0）下面在还原一个数据库（备份文件40多G大小，实际数据库大小300G），在还原过程中，出现一直等待ASYNC_IO_COMPLETION，如下测试截图所示，已经等待了72分钟了，但是还原比例依然为0%
SELECT r.session_id ,
r.command ,
r.start_time,
r.status,
r.wait_type,
CONVERT(NUMERIC(6, 2), r.percent_complete) AS [Percent Complete(%)] ,
CONVERT(VARCHAR(20), DATEADD(ms, r.estimated_completion_time,
GETDATE()), 20) AS [ETA Completion Time] ,
CONVERT(NUMERIC(10, 2), r.total_elapsed_time / 1000.0 / 60.0) AS [Elapsed Min] ,
CONVERT(NUMERIC(10, 2), r.estimated_completion_time / 1000.0 / 60.0) AS [ETA Min] ,
CONVERT(NUMERIC(10, 2), r.estimated_completion_time / 1000.0 / 60.0
/ 60.0) AS [ETA Hours] ,
CONVERT(VARCHAR(1000), ( SELECT SUBSTRING(text,
r.statement_start_offset / 2,
CASE WHEN r.statement_end_offset = -1
THEN 1000
ELSE ( r.statement_end_offset
- r.statement_start_offset )
/ 2
END)
FROM sys.dm_exec_sql_text(sql_handle)
)) AS CommandText
FROM sys.dm_exec_requests r
WHERE command IN ( 'RESTORE DATABASE', 'BACKUP DATABASE','RESTORE LOG' );