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So I had a few servers with 8 drives configured in RAID 10. Four pairs of two drives in the RAID1 level. One of the drives went bad and the RAID controller removed one pair from the set, so it now only contains 6 drives and but it's marked as online. The bad drive was marked as UBad, the good one as UGood. I replaced the bad drive, but now I realized it's not possible to add them back to the RAID10 setup. Is there any way around it? How is it possible the controller could reduce the number of drives, but not add more?

This is the layout:

------------------------------------------------------------------------------
DG Arr Row EID:Slot DID Type   State BT       Size PDC  PI SED DS3  FSpace TR 
------------------------------------------------------------------------------
 0 -   -   -        -   RAID10 Optl  N    2.044 TB dflt N  N   none N      N  
 0 0   -   -        -   RAID1  Optl  N  698.125 GB dflt N  N   none N      N  
 0 0   0   252:0    14  DRIVE  Onln  N  698.125 GB dflt N  N   none -      N  
 0 0   1   252:2    10  DRIVE  Onln  N  698.125 GB dflt N  N   none -      N  
 0 1   -   -        -   RAID1  Optl  N  698.125 GB dflt N  N   none N      N  
 0 1   0   252:3    11  DRIVE  Onln  N  698.125 GB dflt N  N   none -      N  
 0 1   1   252:4    16  DRIVE  Onln  N  698.125 GB dflt N  N   none -      N  
 0 2   -   -        -   RAID1  Optl  N  698.125 GB dflt N  N   none N      N  
 0 2   0   252:5    17  DRIVE  Onln  N  698.125 GB dflt N  N   none -      N  
 0 2   1   252:7    12  DRIVE  Onln  N  698.125 GB dflt N  N   none -      N  
------------------------------------------------------------------------------

And drives after replacing the bad one:

------------------------------------------------------------------------------------
EID:Slt DID State DG       Size Intf Med SED PI SeSz Model                  Sp Type 
------------------------------------------------------------------------------------
252:0    14 Onln   0 698.125 GB SATA HDD N   N  512B WDC WD7500BPKT-75PK4T0 U  -    
252:1    15 UGood  -   931.0 GB SATA HDD N   N  512B ST91000640NS           D  -    
252:2    10 Onln   0 698.125 GB SATA HDD N   N  512B WDC WD7500BPKT-00PK4T0 U  -    
252:3    11 Onln   0 698.125 GB SATA HDD N   N  512B WDC WD7500BPKT-75PK4T0 U  -    
252:4    16 Onln   0 698.125 GB SATA HDD N   N  512B WDC WD7500BPKX-22HPJT0 U  -    
252:5    17 Onln   0 698.125 GB SATA HDD N   N  512B WDC WD7500BPKX-22HPJT0 U  -    
252:6    13 UGood  - 698.125 GB SATA HDD N   N  512B WDC WD7500BPKX-22HPJT0 D  -    
252:7    12 Onln   0 698.125 GB SATA HDD N   N  512B WDC WD7500BPKX-22HPJT0 U  -    
------------------------------------------------------------------------------------

Before the change, the drive in slot 252:1 was marked as UBad.

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    In a true RAID10 array, a single failed drive should not remove an entire RAID1 pair/set. Are you sure you are not running RAID 0+1? Can you show your RAID layout and status? – shodanshok Jun 11 '18 at 10:58
  • If you tell us what OS and which RAID card you're using, I can give you some commands to produce data on layout and status. – Spooler Jun 11 '18 at 15:47
  • Added the data to the question. – Lukáš Lalinský Jun 12 '18 at 9:13
  • You should add the RAID controller model and maker. It's difficult to explain the behavior without knowing that information. Did the controller remove the bad array on it's own or did you do it while replacing the bad drive? – Leo Jun 13 '18 at 23:11

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