Mdadm raid5/dev/md0 lost a disk and recovery from another machine

CentOS-How to add a new disk into a mdadm raid5/dev/md0 whick lost A/DEV/SDC1 disk and revoery at another m Achine?

Fdisk-l--stop/dev/md0
# to force active the raid by Remaind 3 disks.   -A--force/dev/md0/dev/sdb1/dev/sde1/dev/sdd1
# Add a new disk into/dev/md0--manage/dev/md0--add/dev/sdc1

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We build a/dev/md0 on a Unitek (removeable USB Storadge with 4 disks inside) by Mdadm software, and mdadm-create/dev/ MD0 operated on a HUAWEI server, our recovery work is done on my laptop, and we meet many many problems, during recovery.

We miss a disk--/DEV/SDC1 from the raid/dev/md0, and now has a new disk--same compable with the LOST/DEV/SBC1, on Ha nd.

And then we Joury is startiing

• Check/dev List

ll/dev/

Nothing about/dev/md0.

• CHECK/DEV/MD0 State:

Cat/proc/mdstat

<none>

... nothing (for the totally new machine to the/dev/md0 no conf file, no superblock ...)

• We try force Mdadm to assembly to force Mdadm Auto Recovery itself:

mdadm --assemble--run --force/dev/md0

Mdadm-a--FORCE/DEV/MD0/DEV/SDB1/DEV/SDE1/DEV/SDD1

We get "can ' t open/dev/md0 array info" or "/DEV/SDB1 is busying" and many other error response info;

• Then we try to add a new disk into

Mdadm--manage/dev/md0--add/dev/info for/dev/md0

• Try get into manage mode, can ' t get config file

[Email protected] dev]# mdadm--assemble/dev/md0--scan--force
Mdadm:/dev/md0 not identified in config file.

• A key operated is coming, and leads us to a success result.
  All the steps above, we don't stop the/dev/md0 and get many wrong try and get many failed resulte.

Mdadm--stop/dev/md0
Mdadm:stopped/dev/md0

[Email protected] dev]# mdadm--assemble/dev/md0--scan--infilecat / proc/<none>

Mdadm--force start by remain 3 disks, and add a new disk into/dev/md0, and get to recovery state.

[Email protected] dev]#mdadm-a--force/dev/md0/dev/sdb1/dev/sde1/dev/ sdd1mdadm:/dev/md0 have been started with3Drives (out of4). [Email protected] dev]# mdadm --manage/dev/md0--add/dev/ sdc1 mdadm:added/dev/Sdc1[[email protected] dev]#Cat/proc/mdstat personalities: [RAID6] [RAID5] [raid4] md0:active RAID5 sdc1[5] Sdd1[0] Sde1[4] Sdb1[2]      8790402048Blocks Super1.2Level5, 512k Chunk, algorithm2[4/3] [U_uu] [...............] Recovery =0.0% (184776/2930134016) finish=1321.3min speed=36955k/sec Bitmap:0/ Apages [0KB], 65536KB chunkunused devices:<none>

Conclusion:

• Remember to stop/dev/md0 at first step, then do other operates;
• MDADM Create RAID5 array, every RAID array info were storaged at every physical disk, no matter what their position was Ch Anged, Madadm can recognize the correct RAID array info.
• Mdadm is realy a stronger sofeware at protect our data, if use correctly we need not worry on our data ' s safety---if Only lost one disk, we can find them back;

-----Other Relate Info reference

1. http://blog.csdn.net/waityoualife/article/details/5612243

Mdadm raid5/dev/md0 lost a disk and recovery from another machine