What Happens When Hard Disk Fails in RAID 5

Q. What happens when a hard disk fails in RAID 5? How many hard drive can fail in RAID 5?

A. RAID is acronym for Redundant Array of Independent Disks, also known as Redundant Array of Inexpensive Disks. It is use to increase reliability. You combine multiple physical hard disks into groups (arrays) that work as a single logical disk i.e. this array of drives appears to the computer as a single logical storage unit or drive.


RAID-5 features

RAID level 5 has following features:

  1. Striping with distributed parity
  2. Fault tolerance supported
  3. Redundancy supported (parity)
  4. Hot spare option supported
  5. Minimum 3 or more disk needed
  6. Performance: Good
  7. Protection: Good (if any disk fails data can be recovered)
  8. Above characteristics makes RAID 5 popular and is well suited to transaction oriented environments.

What happens when hard disk fails in raid 5

  • Because of parity, information all data are available in case one of the disks fails. If extra (spare) disks are available, then reconstruction will begin immediately after the device failure.
  • However if two hard disks fail at same time, all data are LOST.
  • In short RAID 5 can survive one disk failure, but not two or more.

Update: See why RAID 10 is better choice for database server instead of RAID 5 for performance and reliability.

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63 comments… add one
  • Subrat Sep 23, 2013 @ 15:24

    i have 28 hard disk with raid technology and with 02 hard disk drive failure the system still working. further if i remove three and inserted the same in different slot it will work? and if i replace these three with new one is system work or not?

  • DanLara Nov 6, 2013 @ 21:35

    I’m working on a Dell PowerEdge 2800 with RAID5. one of the disks failed and I replace it with a new identical one. power up the server and the light on it still amber after 24 hours. installed open managed an it still shows the status of the drive as “failed”. Did I need to do something else? I thought the drive would be rebuild automatically?
    Any ideas?

  • dana Feb 10, 2015 @ 0:20

    I have a server HP DL380 G8 and I have two hard disk configured as a mirror . one of the hard disk was faild , but still the server is working fine in one hard disk , I add a new hard disk with the same size but still I cannot see the new hard disk my be need to add under the Mirror , my Q is its possible boot from smart CD and add new hard disk under raid configuration without losing the system configuration. ?

  • Murzeeth May 5, 2015 @ 10:39

    2 days back i had a problem server hard disk and server won’t boot. I have IBM system X3650 series server with 3 x 73.4 GB SAS 3.5″ hard disk with Raid5. After the weekend holiday when i came to office server was down and hard disk 0 is in critical. i tried to reboot unfortunately it won’t. i bought the same size and modelled hard disk and insert the same to the server. Initially it was giving error and i went through the IBM serveraid 8k controller and it rebuilds. After rebuilds the restarted and giving the error A DISK READ ERROR OCCURED PRESS CTL + ALT+ DEL TO RESTART. Keeps on showing the same message on each restarts and server not boot.

    Please guide me what should i do?

  • Psunday May 11, 2015 @ 10:13

    Hi Guyz, plz I have dl 380 g8 server that have 8TB HDD on bay1 and 8TB HDD on bay 2. I used RAID 1 for OS (1st and 2nd slot) the remaining 6TB HDD on bay 1, I used RAID 5. Guy, which appropriate raid can I use for 8TB HDD at the 2nd bay to achieve 14TB HDD. (6TB bay 1 plus 8TB HDD bay 2)?


  • kelly Oct 15, 2015 @ 7:03

    i have problem with my xitrix, raid 5, i had 12 pcs HDD with 3TB. my problem is the first HDD is damage… can i still replace this 1st HDD and back to normal or still needed for any settings or configuration to fixed this problem? my OS is windows 2008 server. we used hardware raid., my 2nd question is some of the opinion i get is that they said the OS is being installed at 1st HDD. :( your feedback is highly appreciated..



  • Rasmus Christensen Jan 5, 2016 @ 14:58

    Hello guys.

    I know that this Q may have been asked before… :-)

    Imagine that i have a BOX with 9 300GB 10K SAS drives.

    ||| __ __ __ __ __ __ __ __ __ |||
    ||| 1 2 3 4 5 6 7 8 9 |||
    |———————————–| HS
    RAID 5

    Disk 1-8 runs RAID5 and disk 9 is hot-spare… Disk 4 dies and the hot-spare jumps in and is bieng rebuild as disk 4… Now disk 4 is “By-passed” by IBM DS Storage Manager and DSM says that i cannot take out disk 4… Then on a forum, people writes that i can do something like “Force fail disk” i know this feature, but i can’t use it…

    What the hell do a wise one do here…?

    If i kill the hot-spare disk, then i can “Force Fail” disk 4 and replace it, but if any other disk failes when the rebuild is running, then i’m skrewed…

    • parveen Apr 22, 2016 @ 11:53

      my question is if i have server 2008 and my server got corrupt means.Now Window server hard disk not working.Its got damage system not getting ON now how i can take the my Active directory backup.Which i have its a old backup.So guys tell me now what i can do for AD backu.rember system not getting on means HD got damage.every think i did with hd repair and all that still its in same condition now rply the ans….plzzzzzzz

  • Neppet Jan 23, 2017 @ 6:40

    I have IBM Storwize V3700 with one failed drive in RAID 5 array. We don’t have spares to replace the drive immediately. Is it ok to let storage run with one failed drive or is there a possibility that parity is overwritten if I let users to use the storage?

    Also, does replacement drive need to have EXACTLY the same firmware level as the original? Or is it enough that model and size are the same?

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