哈哈，终于遇到了传说中软RAID！

检查一台服务器是否有配置RAID。先dmesg看有没有RAID卡：

# dmesg|grep -i raid
ahci 0000:00:1f.2: AHCI 0001.0100 32 slots 4 ports 3 Gbps 0xf impl RAID mode
device-mapper: dm-raid45: initialized v0.2594l
md: Autodetecting RAID arrays.

看来是有的，只是看不出来是哪种RAID卡（0000:00:1f.2？）。接着fdisk，发现有两块硬盘/dev/sda，/dev/sdb：

# fdisk -l

Disk /dev/sda: 250.0 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux
/dev/sda2              14        1318    10482412+  83  Linux
/dev/sda3            1319        4189    23061307+   5  Extended
/dev/sda4            4190       30400   210539857+  83  Linux
/dev/sda5            1319        2623    10482381   83  Linux
/dev/sda6            2624        3928    10482381   83  Linux
/dev/sda7            3929        4189     2096451   82  Linux swap / Solaris

Disk /dev/sdb: 250.0 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          13      104391   83  Linux
/dev/sdb2              14        1318    10482412+  83  Linux
/dev/sdb3            1319        4189    23061307+   5  Extended
/dev/sdb4            4190       30400   210539857+  83  Linux
/dev/sdb5            1319        2623    10482381   83  Linux
/dev/sdb6            2624        3928    10482381   83  Linux
/dev/sdb7            3929        4189     2096451   82  Linux swap / Solaris

而且这两块硬盘都是物理硬盘：

# hdparm -i /dev/sda

/dev/sda:

 Model=ST3250310AS                             , FwRev=3.AAB   , SerialNo=            6RY8ZABB
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs RotSpdTol>.5% }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=unknown, BuffSize=8192kB, MaxMultSect=16, MultSect=?16?
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=268435455
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4
 DMA modes:  mdma0 mdma1 mdma2
 UDMA modes: udma0 udma1 udma2
 AdvancedPM=no WriteCache=enabled
 Drive conforms to: Unspecified:  ATA/ATAPI-3 ATA/ATAPI-4 ATA/ATAPI-5 ATA/ATAPI-6 ATA/ATAPI-7

 * signifies the current active mode

# hdparm -i /dev/sdb

/dev/sdb:

 Model=ST3250310AS                             , FwRev=3.AAB   , SerialNo=            6RY6QYSJ
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs RotSpdTol>.5% }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=unknown, BuffSize=8192kB, MaxMultSect=16, MultSect=?16?
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=268435455
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4
 DMA modes:  mdma0 mdma1 mdma2
 UDMA modes: udma0 udma1 udma2
 AdvancedPM=no WriteCache=enabled
 Drive conforms to: Unspecified:  ATA/ATAPI-1 ATA/ATAPI-2 ATA/ATAPI-3 ATA/ATAPI-4 ATA/ATAPI-5 ATA/ATAPI-6 ATA/ATAPI-7

 * signifies the current active mode

看来没有配RAID。于是df，结果发现只列出了一块硬盘，而且这块硬盘既不是/dev/sda也不是/dev/sdb，而是/dev/mapper/isw_ddjafhgbch_Volume0：

[root@localhost device-mapper-1.02.39]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/isw_ddjafhgbch_Volume0p6
                      9.7G  6.2G  3.0G  68% /
/dev/mapper/isw_ddjafhgbch_Volume0p2
                      195G  115G   71G  62% /home
/dev/mapper/isw_ddjafhgbch_Volume0p5
                      9.7G  664M  8.6G   8% /var
/dev/mapper/isw_ddjafhgbch_Volume0p3
                      9.7G  152M  9.1G   2% /tmp
/dev/mapper/isw_ddjafhgbch_Volume0p1
                       99M   12M   83M  13% /boot
tmpfs                 2.0G     0  2.0G   0% /dev/shm

这就奇怪了：如果服务器有配RAID，那么fdisk应该只能列出一块硬盘；如果服务器没有配RAID，那么fdisk的结果应该与df的结果一致。

难道这是传说中的软RAID？

于是拿之前的RAID卡信息去搜索...后来找到了lvm，而且服务器也有安装lvm2:

# rpm -qa|grep lvm
lvm2-2.02.56-8.el5
system-config-lvm-1.1.5-4.el5

尝试执行lvm的相关指令（pvs\vgs\lvs），但这些命令没有任何输出：

# pvs
# lvs
# vgs
#

后来发现，如果服务器有配置lvm，那么fdisk出来的分区类型应该是8e。而此服务器的分区类型是83：

 Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux

 Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          13      104391   83  Linux

看来服务器并不是通过lvm配置的RAID。

继续搜索...后来找到了Device Mapper及其对应的管理工具dmsetup。于是尝试使用dmsetup的相关指令，发现竟然有反应：

[root@localhost device-mapper-1.02.39]# dmsetup table
isw_ddjafhgbch_Volume0p7: 0 4192902 linear 253:0 63103383
isw_ddjafhgbch_Volume0p6: 0 20964762 linear 253:0 42138558
isw_ddjafhgbch_Volume0p5: 0 20964762 linear 253:0 21173733
isw_ddjafhgbch_Volume0: 0 488390392 mirror core 3 131072 nosync block_on_error 2 8:0 0 8:16 0
isw_ddjafhgbch_Volume0p3: 0 20964825 linear 253:0 208845
isw_ddjafhgbch_Volume0p2: 0 421079715 linear 253:0 67296285
isw_ddjafhgbch_Volume0p1: 0 208782 linear 253:0 63

看来服务器就是是通过Device Mapper配置的软RAID(mirror，相当于RAID 1)。

后来进一步了解，Device mapper 是 Linux 2.6 内核中提供的一种从逻辑设备到物理设备的映射框架机制，在该机制下，可以实现软RAID。之前找到的lvm也是基与此机制而扩展出来的应用...

另外，除了通过dmsetup table查看RAID类型外，还可以通过dmsetup info查看RAID状态：

[root@localhost device-mapper-1.02.39]# dmsetup info
Name:              isw_ddjafhgbch_Volume0p7
State:             ACTIVE
Read Ahead:        256
Tables present:    LIVE
Open count:        1
Event number:      0
Major, minor:      253, 6
Number of targets: 1
UUID: part7-DMRAID-isw_ddjafhgbch_Volume0

Name:              isw_ddjafhgbch_Volume0p6
State:             ACTIVE
Read Ahead:        256
Tables present:    LIVE
Open count:        1
Event number:      0
Major, minor:      253, 5
Number of targets: 1
UUID: part6-DMRAID-isw_ddjafhgbch_Volume0

...