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Hardware Thread, Drives failure in Raid 5 in Technical; Dear all My question is that if i configure Raid 5 with 3 hard drives and if 2 of them ...
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    Drives failure in Raid 5

    Dear all

    My question is that if i configure Raid 5 with 3 hard drives and if 2 of them fails
    will it be possible to recover data Thanks.

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    Steve21's Avatar
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    Quote Originally Posted by labist View Post
    Dear all

    My question is that if i configure Raid 5 with 3 hard drives and if 2 of them fails
    will it be possible to recover data Thanks.
    With 2 disks down no it's not. With 1 down yes it is.

    Steve

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    fiza's Avatar
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    Always have a hot spare

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    sonofsanta's Avatar
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    No. Even with a hot spare as well, a second drive could fail whilst the array was rebuilding. The only true protection against two-disk failure is RAID 6.

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    AButters's Avatar
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    Yes but the chances of two drives failing within 24 hours are slim. Possible but slim. Raid 6 has nasty write overheads. I used to run it but don't any more gone back to raid 5 + hospare for most things.

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    It's scary stuff hot-swapping a RAID 5 drive, but I have done it and survived! It wasn't difficult; it's just the awful hoping that what I'm doing won't affect anything else! As others have said, it would be really bad luck to lose 2 in short succession.

    Nothing is impossible, so it could happen, but hopefully it won't (Said she clutching the nearest piece of wood with crossed fingers)

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    danbuntu's Avatar
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    Quote Originally Posted by sonofsanta View Post
    No. Even with a hot spare as well, a second drive could fail whilst the array was rebuilding. The only true protection against two-disk failure is RAID 6.
    or raid 5 with more disks

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    plexer's Avatar
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    Quote Originally Posted by danbuntu View Post
    or raid 5 with more disks
    Nope RAID5 with more disks still only protects you against one failure and the more drives you have the bigger your array the longer your rebuild time and the higher chance of more failures.

    Ben

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    danbuntu's Avatar
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    ahh yes my bad

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    jamesfed's Avatar
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    Lets remember that just RAID on its own (even RAID6) isn't 100% sure that you won't loose data at some stage due to drive failure/ect.

    No system will ever be 100% but a good backup system is always a must - ideally a mix of both disk (for high speed backup/restore) and tape (for offsite).

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    Quote Originally Posted by plexer View Post
    Nope RAID5 with more disks still only protects you against one failure and the more drives you have the bigger your array the longer your rebuild time and the higher chance of more failures.

    Ben
    Raid5
    But more drives mean the array keeps working if one fails, without redundancy and with a performance hit though.

    It might depend on the controller but from experience if a single drive fails in a 3 drive raid5 array the server will crash and you can't use the array until the faulty drive has been replaced and the array rebuilt.

    If on the other hand a single drive fails in a 5 disk raid5 array the server keeps running and the array should rebuild in the background when the faulty drive is replaced - dont ask me about a 4 disk array because I dont know.

    So if you can go for a 5 disk array +1hotspare +1sat on a shelf

    Raid5 only gives you redundancy it still needs a backup solution because if 2 drives fail you can wave goodbye to your data.

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    How about RAID 5EE using five disks?

    NN

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    How about RAID 5EE using five disks?

    NN

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    sonofsanta's Avatar
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    Quote Originally Posted by ToyHeartsFan View Post
    It might depend on the controller but from experience if a single drive fails in a 3 drive raid5 array the server will crash and you can't use the array until the faulty drive has been replaced and the array rebuilt.
    I don't think that should happen - the whole point of RAID 5 is you can lose a disk and still keep running. More disks in RAID5 is actually a greater threat, as others have said, as it increases the odds of a disk failing while you're still recovering the missing disk. A hot spare is not really any greater protection, other than the fact that it reduces the time from "disk goes wrong" to "array rebuilding" to effectively zero, rather than the variable "when you notice" time span.

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    Quote Originally Posted by AButters View Post
    Yes but the chances of two drives failing within 24 hours are slim. Possible but slim. Raid 6 has nasty write overheads. I used to run it but don't any more gone back to raid 5 + hospare for most things.
    Yep, slim, but can happen. Member of my team here had his Raid5 fail at home, only for a 2nd disk to fail while the 1st disk was still rebuilding!.

    Like others have said, still need to have a backup solution, just in case that 1 in a million happens, and 2 disks fail.

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