Disk /dev/mapper/olddata-home: 176.9 GB, 176898965504 bytes, 345505792 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

客戶的服務器，突然開不了機，大概是磁盤有問題。讓機房重新找個磁盤，重裝centos 7，裝完后，把這個舊磁盤掛載上去。結果在掛載磁盤的過程中，提示：

[root@localhost /]# mount /dev/mapper/olddata-home /data3
mount: mount /dev/mapper/olddata-home on /data3 failed: Structure needs cleaning

客戶有100多G的數據，沒有備份，只能是活馬當死馬醫了。其實這種情況的出現，很可能是機房意外斷電，導致系統沒有正常關機，系統日志有點問題，導致系統無法啟動，修復下磁盤按說是可以解決問題的。

xfs_repair -L /dev/mapper/olddata-home

執行了上面的命令，修復文件系統，下面是執行過程：

[root@localhost /]# xfs_repair -L /dev/mapper/olddata-home
Phase 1 - find and verify superblock...
Phase 2 - using internal log
        - zero log...
ALERT: The filesystem has valuable metadata changes in a log which is being
destroyed because the -L option was used.
        - scan filesystem freespace and inode maps...
Metadata CRC error detected at xfs_allocbt block 0xfaffc38/0x1000
btree block 3/507783 is suspect, error -74
bad magic # 0x340cb973 in btcnt block 3/507783
agf_freeblks 4963941, counted 4963401 in ag 3
agf_btreeblks 563, counted 562 in ag 3
sb_ifree 183157, counted 144647
sb_fdblocks 21552161, counted 21269479
        - found root inode chunk
Phase 3 - for each AG...
        - scan and clear agi unlinked lists...
        - process known inodes and perform inode discovery...
        - agno = 0
        - agno = 1
        - agno = 2
        - agno = 3
        - process newly discovered inodes...
Phase 4 - check for duplicate blocks...
        - setting up duplicate extent list...
        - check for inodes claiming duplicate blocks...
        - agno = 0
        - agno = 3
        - agno = 2
        - agno = 1
Phase 5 - rebuild AG headers and trees...
        - reset superblock...
Phase 6 - check inode connectivity...
        - resetting contents of realtime bitmap and summary inodes
        - traversing filesystem ...
        - traversal finished ...
        - moving disconnected inodes to lost+found ...
Phase 7 - verify and correct link counts...
Maximum metadata LSN (1329113463:-1024357339) is ahead of log (1:2).
Format log to cycle 1329113466.
done
[root@localhost /]#mount /dev/mapper/olddata-home /data3

然后就可以用命令掛載磁盤了，完美解決。