RAID5 array with 3 drives (1 failed)

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feanorarcamenel

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May 8, 2017
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I have lost one of the drives due to bad sector in a RAID5 array with 3 drives. As a result, the array became inactive.

When I tried to recreate the array with the following command:
sudo mdadm --assemble --force /dev/md0 /dev/sdc1 /dev/sdd1 /dev/sde1
Click to expand...
it could activate the array with a State : clean, degraded. Below is the output of "sudo mdadm -D /dev/md0":

/dev/md0:
Version : 1.2
Creation Time : Mon May 8 15:12:01 2017
Raid Level : raid5
Array Size : 7813771264 (7451.79 GiB 8001.30 GB)
Used Dev Size : 3906885632 (3725.90 GiB 4000.65 GB)
Raid Devices : 3
Total Devices : 2
Persistence : Superblock is persistent

Intent Bitmap : Internal

Update Time : Mon May 8 17:24:24 2017
State : clean, degraded
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Layout : left-symmetric
Chunk Size : 512K

Name : ubuntuBox:0 (local to host ubuntuBox)
UUID : 95c275e4:1b78840f:10f5974b:fe142ac8
Events : 60

Number Major Minor RaidDevice State
0 8 33 0 active sync /dev/sdc1
2 0 0 2 removed
2 8 65 2 active sync /dev/sde1
Click to expand...

When I mount this device, I can reach only part of my files. Luckily, I have backup of a large part of the missing files, except for the most recent ones. However, I would like to ask if there is a way to save the raid array by getting a new healthy array.

Here is the output for "cat /proc/mdstat":

Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10]
md0 : active raid5 sdc1[0] sde1[2]
7813771264 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/2] [U_U]
bitmap: 0/30 pages [0KB], 65536KB chunk

unused devices: <none>
Click to expand...


This is the output for "sudo mdadm --examine /dev/sd[cde]1":

/dev/sdc1:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x1
Array UUID : 95c275e4:1b78840f:10f5974b:fe142ac8
Name : ubuntuBox:0 (local to host ubuntuBox)
Creation Time : Mon May 8 15:12:01 2017
Raid Level : raid5
Raid Devices : 3

Avail Dev Size : 7813771264 (3725.90 GiB 4000.65 GB)
Array Size : 7813771264 (7451.79 GiB 8001.30 GB)
Data Offset : 262144 sectors
Super Offset : 8 sectors
Unused Space : before=262056 sectors, after=0 sectors
State : clean
Device UUID : 3e1f8352:8b51d20b:d13f2301:0c25ed92

Internal Bitmap : 8 sectors from superblock
Update Time : Mon May 8 17:24:24 2017
Bad Block Log : 512 entries available at offset 72 sectors
Checksum : ef119df - correct
Events : 60

Layout : left-symmetric
Chunk Size : 512K

Device Role : Active device 0
Array State : A.A ('A' == active, '.' == missing, 'R' == replacing)

/dev/sdd1:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x3
Array UUID : 95c275e4:1b78840f:10f5974b:fe142ac8
Name : ubuntuBox:0 (local to host ubuntuBox)
Creation Time : Mon May 8 15:12:01 2017
Raid Level : raid5
Raid Devices : 3

Avail Dev Size : 7813771264 (3725.90 GiB 4000.65 GB)
Array Size : 7813771264 (7451.79 GiB 8001.30 GB)
Data Offset : 262144 sectors
Super Offset : 8 sectors
Recovery Offset : 0 sectors
Unused Space : before=262056 sectors, after=0 sectors
State : clean
Device UUID : e4a6bbbb:f34c95db:29f02738:f9ac2358

Internal Bitmap : 8 sectors from superblock
Update Time : Mon May 8 15:17:40 2017
Bad Block Log : 512 entries available at offset 72 sectors
Checksum : 442ab759 - correct
Events : 18

Layout : left-symmetric
Chunk Size : 512K

Device Role : Active device 1
Array State : AAA ('A' == active, '.' == missing, 'R' == replacing)

/dev/sde1:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x1
Array UUID : 95c275e4:1b78840f:10f5974b:fe142ac8
Name : ubuntuBox:0 (local to host ubuntuBox)
Creation Time : Mon May 8 15:12:01 2017
Raid Level : raid5
Raid Devices : 3

Avail Dev Size : 7813771264 (3725.90 GiB 4000.65 GB)
Array Size : 7813771264 (7451.79 GiB 8001.30 GB)
Data Offset : 262144 sectors
Super Offset : 8 sectors
Unused Space : before=262056 sectors, after=0 sectors
State : clean
Device UUID : dfee12e5:90d310e9:4719f740:8b5dbf0c

Internal Bitmap : 8 sectors from superblock
Update Time : Mon May 8 17:24:24 2017
Bad Block Log : 512 entries available at offset 72 sectors
Checksum : 38657d7d - correct
Events : 60

Layout : left-symmetric
Chunk Size : 512K

Device Role : Active device 2
Array State : A.A ('A' == active, '.' == missing, 'R' == replacing)
Click to expand...
 
Solution
D
The RAID should not become inactive just because of a single drive failure. Did you run mdadm --examine before you tried the forced mount? At that point, you might have been able to figure out which drive went offline when. Now you have altered the RAID META data.

Disclaimer: Professional data recovery is always the safest route, if the data is of any value at all. A 3 drive RAID 5 should cost somewhere between $750 and $2000 with a reputable data recovery lab that doesn't gouge.

Recommended DIY Steps:

1. Get a full sector-by-sector clone of each drive using gnu ddrescue (this is both a way to test all the drive, make sure you have a backup and provide physically healthy clones to work with on step 2)
2. Use a data recovery...
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D

DR_Luke

Honorable
Dec 1, 2016
363
0
11,160
The RAID should not become inactive just because of a single drive failure. Did you run mdadm --examine before you tried the forced mount? At that point, you might have been able to figure out which drive went offline when. Now you have altered the RAID META data.

Disclaimer: Professional data recovery is always the safest route, if the data is of any value at all. A 3 drive RAID 5 should cost somewhere between $750 and $2000 with a reputable data recovery lab that doesn't gouge.

Recommended DIY Steps:

1. Get a full sector-by-sector clone of each drive using gnu ddrescue (this is both a way to test all the drive, make sure you have a backup and provide physically healthy clones to work with on step 2)
2. Use a data recovery program like R-Studio to virtually reconstruct the RAID using different drive combinations (0,1,2 - 0,1,x - 0,x,2 - x,1,2) to figure out which is the best combination giving the cleanest recovery results.
3. Save the recovered files out to another healthy destination

Good luck!
 
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