曾经道听途说，Linux下的磁盘设备号（/dev/sda、/dev/sdb……）会在操作系统重启后发生编号混乱，尤其是这些磁盘是外置存储盘的时候。最近一次机缘巧合的机会，让我也碰到了这样的情况，做了些简单的实验，找到了些规律。

  1. [root@Smswas1 ~]# fdisk -l


  3. Disk /dev/cciss/c0d0: 146.7 GB, 146778685440 bytes

  4. 255 heads, 63 sectors/track, 17844 cylinders

  5. Units = cylinders of 16065 * 512 = 8225280 bytes


  7. Device Boot Start End Blocks Id System

  8. /dev/cciss/c0d0p1 * 1 13 104391 83 Linux

  9. /dev/cciss/c0d0p2 14 17844 143227507+ 8e Linux LVM


  11. Disk /dev/sda: 107.3 GB, 107374182400 bytes

  12. 255 heads, 63 sectors/track, 13054 cylinders

  13. Units = cylinders of 16065 * 512 = 8225280 bytes


  15. Device Boot Start End Blocks Id System

  16. /dev/sda1 1 13054 104856223+ 5 Extended

  17. /dev/sda5 1 7 56164+ 83 Linux

  18. /dev/sda6 8 616 4891761 83 Linux

  19. /dev/sda7 617 6696 48837568+ 83 Linux


  21. Disk /dev/sdb: 36.3 GB, 36354129920 bytes

  22. 64 heads, 32 sectors/track, 34670 cylinders

  23. Units = cylinders of 2048 * 512 = 1048576 bytes


  25. Device Boot Start End Blocks Id System

  26. /dev/sdb1 1 34670 35502064 5 Extended

  27. /dev/sdb5 1 34670 35502048 83 Linux


  29. Disk /dev/sdc: 107.3 GB, 107374182400 bytes

  30. 255 heads, 63 sectors/track, 13054 cylinders

  31. Units = cylinders of 16065 * 512 = 8225280 bytes


  33. Disk /dev/sdc doesn't contain a valid partition table


  35. Disk /dev/sdd: 107.3 GB, 107374182400 bytes

  36. 255 heads, 63 sectors/track, 13054 cylinders

  37. Units = cylinders of 16065 * 512 = 8225280 bytes


  39. Disk /dev/sdd doesn't contain a valid partition table

  40. [root@Smswas1 ~]# ls -l /dev/disk/by-id

  41. total 0

  42. lrwxrwxrwx 1 root root 9 Jun 16 19:14 scsi-1HITACHI_D60055750011 -> ../../sdc

  43. lrwxrwxrwx 1 root root 9 Jun 16 19:05 scsi-1HITACHI_D60055750012 -> ../../sda

  44. lrwxrwxrwx 1 root root 10 Jun 16 19:05 scsi-1HITACHI_D60055750012-part1 -> ../../sda1

  45. lrwxrwxrwx 1 root root 10 Jun 16 19:05 scsi-1HITACHI_D60055750012-part5 -> ../../sda5

  46. lrwxrwxrwx 1 root root 10 Jun 16 19:05 scsi-1HITACHI_D60055750012-part6 -> ../../sda6

  47. lrwxrwxrwx 1 root root 10 Jun 16 19:05 scsi-1HITACHI_D60055750012-part7 -> ../../sda7

  48. lrwxrwxrwx 1 root root 9 Jun 16 19:18 scsi-1HITACHI_D60055750013 -> ../../sdd

  49. lrwxrwxrwx 1 root root 9 Jun 16 19:05 scsi-1HITACHI_D60055750016 -> ../../sdb

  50. lrwxrwxrwx 1 root root 10 Jun 16 19:05 scsi-1HITACHI_D60055750016-part1 -> ../../sdb1

  51. lrwxrwxrwx 1 root root 10 Jun 16 19:05 scsi-1HITACHI_D60055750016-part5 -> ../../sdb5

  52. [root@Smswas1 ~]# ls -l /dev/disk/by-path

  53. total 0

  54. lrwxrwxrwx 1 root root 10 Jun 16 19:05 pci-0000:00:1f.2-scsi-0:0:0:0 -> ../../scd0

  55. lrwxrwxrwx 1 root root 9 Jun 16 19:05 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0000000000000000 -> ../../sda

  56. lrwxrwxrwx 1 root root 10 Jun 16 19:05 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0000000000000000-part1 -> ../../sda1

  57. lrwxrwxrwx 1 root root 10 Jun 16 19:05 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0000000000000000-part5 -> ../../sda5

  58. lrwxrwxrwx 1 root root 10 Jun 16 19:05 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0000000000000000-part6 -> ../../sda6

  59. lrwxrwxrwx 1 root root 10 Jun 16 19:05 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0000000000000000-part7 -> ../../sda7

  60. lrwxrwxrwx 1 root root 9 Jun 16 19:05 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0001000000000000 -> ../../sdb

  61. lrwxrwxrwx 1 root root 10 Jun 16 19:05 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0001000000000000-part1 -> ../../sdb1

  62. lrwxrwxrwx 1 root root 10 Jun 16 19:05 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0001000000000000-part5 -> ../../sdb5

  63. lrwxrwxrwx 1 root root 9 Jun 16 19:18 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0002000000000000 -> ../../sdd

  64. lrwxrwxrwx 1 root root 9 Jun 16 19:14 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0003000000000000 -> ../../sdc

命令的输出可以看到，有4块从同一光纤通道（pci-0000:0b:00.0-fc-0x50060e800043cd71）认到的存储磁盘sda、sdb、sdc、sdd，操作系统重启后的输出如下：

  1. [root@Smswas1 ~]# fdisk -l


  3. Disk /dev/cciss/c0d0: 146.7 GB, 146778685440 bytes

  4. 255 heads, 63 sectors/track, 17844 cylinders

  5. Units = cylinders of 16065 * 512 = 8225280 bytes


  7. Device Boot Start End Blocks Id System

  8. /dev/cciss/c0d0p1 * 1 13 104391 83 Linux

  9. /dev/cciss/c0d0p2 14 17844 143227507+ 8e Linux LVM


  11. Disk /dev/sda: 107.3 GB, 107374182400 bytes

  12. 255 heads, 63 sectors/track, 13054 cylinders

  13. Units = cylinders of 16065 * 512 = 8225280 bytes


  15. Device Boot Start End Blocks Id System

  16. /dev/sda1 1 13054 104856223+ 5 Extended

  17. /dev/sda5 1 7 56164+ 83 Linux

  18. /dev/sda6 8 616 4891761 83 Linux

  19. /dev/sda7 617 6696 48837568+ 83 Linux


  21. Disk /dev/sdb: 36.3 GB, 36354129920 bytes

  22. 64 heads, 32 sectors/track, 34670 cylinders

  23. Units = cylinders of 2048 * 512 = 1048576 bytes


  25. Device Boot Start End Blocks Id System

  26. /dev/sdb1 1 34670 35502064 5 Extended

  27. /dev/sdb5 1 34670 35502048 83 Linux


  29. Disk /dev/sdc: 107.3 GB, 107374182400 bytes

  30. 255 heads, 63 sectors/track, 13054 cylinders

  31. Units = cylinders of 16065 * 512 = 8225280 bytes


  33. Disk /dev/sdc doesn't contain a valid partition table


  35. Disk /dev/sdd: 107.3 GB, 107374182400 bytes

  36. 255 heads, 63 sectors/track, 13054 cylinders

  37. Units = cylinders of 16065 * 512 = 8225280 bytes


  39. Disk /dev/sdd doesn't contain a valid partition table

  40. [root@Smswas1 ~]# ls -l /dev/disk/by-id

  41. total 0

  42. lrwxrwxrwx 1 root root 9 Jun 16 19:24 scsi-1HITACHI_D60055750011 -> ../../sdd

  43. lrwxrwxrwx 1 root root 9 Jun 16 19:24 scsi-1HITACHI_D60055750012 -> ../../sda

  44. lrwxrwxrwx 1 root root 10 Jun 16 19:24 scsi-1HITACHI_D60055750012-part1 -> ../../sda1

  45. lrwxrwxrwx 1 root root 10 Jun 16 19:24 scsi-1HITACHI_D60055750012-part5 -> ../../sda5

  46. lrwxrwxrwx 1 root root 10 Jun 16 19:24 scsi-1HITACHI_D60055750012-part6 -> ../../sda6

  47. lrwxrwxrwx 1 root root 10 Jun 16 19:24 scsi-1HITACHI_D60055750012-part7 -> ../../sda7

  48. lrwxrwxrwx 1 root root 9 Jun 16 19:24 scsi-1HITACHI_D60055750013 -> ../../sdc

  49. lrwxrwxrwx 1 root root 9 Jun 16 19:24 scsi-1HITACHI_D60055750016 -> ../../sdb

  50. lrwxrwxrwx 1 root root 10 Jun 16 19:24 scsi-1HITACHI_D60055750016-part1 -> ../../sdb1

  51. lrwxrwxrwx 1 root root 10 Jun 16 19:24 scsi-1HITACHI_D60055750016-part5 -> ../../sdb5

  52. [root@Smswas1 ~]# ls -l /dev/disk/by-label

  53. total 0

  54. lrwxrwxrwx 1 root root 18 Jun 16 19:23 boot -> ../../cciss/c0d0p1

  55. [root@Smswas1 ~]# ls -l /dev/disk/by-path

  56. total 0

  57. lrwxrwxrwx 1 root root 10 Jun 16 19:23 pci-0000:00:1f.2-scsi-0:0:0:0 -> ../../scd0

  58. lrwxrwxrwx 1 root root 9 Jun 16 19:24 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0000000000000000 -> ../../sda

  59. lrwxrwxrwx 1 root root 10 Jun 16 19:24 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0000000000000000-part1 -> ../../sda1

  60. lrwxrwxrwx 1 root root 10 Jun 16 19:24 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0000000000000000-part5 -> ../../sda5

  61. lrwxrwxrwx 1 root root 10 Jun 16 19:24 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0000000000000000-part6 -> ../../sda6

  62. lrwxrwxrwx 1 root root 10 Jun 16 19:24 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0000000000000000-part7 -> ../../sda7

  63. lrwxrwxrwx 1 root root 9 Jun 16 19:24 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0001000000000000 -> ../../sdb

  64. lrwxrwxrwx 1 root root 10 Jun 16 19:24 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0001000000000000-part1 -> ../../sdb1

  65. lrwxrwxrwx 1 root root 10 Jun 16 19:24 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0001000000000000-part5 -> ../../sdb5

  66. lrwxrwxrwx 1 root root 9 Jun 16 19:24 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0002000000000000 -> ../../sdc

  67. lrwxrwxrwx 1 root root 9 Jun 16 19:24 pci-0000:0b:00.0-fc-0x50060e800043cd71:0x0003000000000000 -> ../../sdd

  68. [root@Smswas1 ~]# ls -l /dev/disk/by-uuid

请仔细观察上面的蓝色字和红色字的磁盘，你会发现，在操作系统重启后，磁盘的设备编号发生了变化，sdc和sdd对换了。
而且如果你更仔细的观察就会发现，设备编号sdX是由红色字部分决定的，ls -l /dev/disk/by-path的输出决定了sdX的编号，换句话说，sdX的编号是由“光纤卡的物理位置+光纤卡的WWN+映射到主机的LUN ID”决定的。
如果想判断重启后，sdX的编号是否会发生变化，只要ls -l /dev/disk/by-path的输出即可。