Question about hardware RAID card failure running RAID 1

Discussion in 'SSDs & Data Storage' started by rigurat, Dec 28, 2013.

  1. rigurat

    rigurat Limp Gawd

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    I understand all data is lost if the RAID card fails while runing RAID 0, 5 or 6 but what about if it was running RAID 1, where all the data isn't scattered accross multiple disks. For RAID 1, all the data is in one disc, just like a regular stand alone drive, but would it still behave like that if hooked up to a different PC?

    Would you be able to remove the drives and put them in another PC and run it regularly? Or do these cards say LSI still use proprietary storage methods, even for RAID 1?
     
    Last edited: Apr 18, 2015
  2. stormy1

    stormy1 [H]ard|Gawd

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    "I understand all data is lost if the RAID card fails while runing RAID 1, 5 or 6 but what about if it was running RAID 1, since all the data isn't scattered on the disks."

    Where did you hear that?
    That is not true, you can replace the card with the same card or certain cards from the same maker and they will in a lot of cases work fine unless the data was corrupted by the old card(which is one of the reasons why you have backups).
     
  3. rigurat

    rigurat Limp Gawd

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    Sorry it seems I made a typo on my previous post, on the first sentence I meant RAID 0 not 1.

    I heard hardware raid cards can be a single point of failure on various "hardware vs software raid" articles and forum discussions.

    Isn't that why we have dual port SAS drives? So we can hook up two controllers to one drive in case one controller fails?
     
    Last edited: Dec 28, 2013
  4. Old Hippie

    Old Hippie [H]ardness Supreme

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    Everyone knows that RAID, of any kind, is not a backup.

    RAID means a redundant array of independent disks used for increased uptime in some situations and isn't meant to be a backup.

    Normally a compatible controller card can read the info and rebuild the array if the drives aren't faulty but if a drive is faulty that's why you need a backup.

    I doubt you are running a commercial website or some mission critical service so backup your data.

    Good luck!
     
  5. Team Merica

    Team Merica [H]Lite

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    RAID 1 is sort-of unique in the sense that each disk is simply a copy of the other. If you have 4 disks in a RAID 1 setup, all four are the same. If one dies you simply take that out, put a new one in, and the RAID processor (hardware card, or your CPU) will copy one of the other disks to your new disk. RAID 1 is also unique in the sense that you can even take these disks out and then run it or boot from it in normal SATA operation.

    The other RAID levels are not like that at all. They require sector formatting by the RAID processor and in many cases the disks cannot be transferred to another family or brand of RAID controller. For example, you may be able to migrate an array from an old Highpoint card to a newer Highpoint card, but not necessarily! It is not usually possible to transfer from an old Highpoint card to a new LSI card, for example.

    EDIT: you can almost always find another RAID controller of the same type/processor on ebay or random websites if you buy major name brand - they're out there.
     
    Last edited: Dec 28, 2013
  6. Team Merica

    Team Merica [H]Lite

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    Also, all data is not lost on RAID 5 or RAID 6 if a single disk fails the array. You can rebuild a single disk from the redundancy built into the other disks. If you suffer an additional failure during the rebuild, you will probably lose required pieces of redundancy and may lose your data - but not necessarily.

    We had a 8 disk RAID 5 array suffer a 2-disk failure at work. The RAID controller would not rebuild it, but we sent the disks to data recovery specialists and got a workable copy of a backup out of it.
     
  7. Old Hippie

    Old Hippie [H]ardness Supreme

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    .

    That's just plain incorrect.

    There is no OS on any RAID disk.

    You'll be able to read the data but the problem is corrupt/incomplete/computer viruses/whatever will be copied to every disk.
     
  8. omniscence

    omniscence [H]ard|Gawd

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    What the RAID controller does with the disks has nothing to do with filesystems, they operate entirely on block level. The pattern that RAID controllers use to distribute data across the disks is normally pretty deterministic, although often not documented.
    However, even if a card dies and there is no compatible replacement anymore, data rescue companies usually have the required information to restore the data on these arrays.
     
  9. Team Merica

    Team Merica [H]Lite

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    I am sorry! I know for a fact if you have a motherboard array (like a Dell PC) and you make a RAID 1 array... and you select and install Windows to that array... you can later transfer a single disk out of that array to another Dell PC and run it in normal SATA operation and it will boot.

    Also, I'm currently booting the computer I'm typing this post from on a RAID array. It's not RAID 1, but it's bootable.

    The point you make about viruses/whatever is true, but best practices and proper form are not really what the OP was asking about.
     
  10. stormy1

    stormy1 [H]ard|Gawd

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    Yes, a raid card can be a single point of failure and duel port drives allow you to hook up 2 controllers to the same drive.
    It is used in place of 5-1 and 6-1 raid (mirrored raid 5/6 arrays) setups to meet check-boxes for regulatory compliance.
    If my opinion it is a stupid solution because the drives are much more likely to fail than controllers but it makes the MBA's happy because it costs less and they can check the item off the list.
    Who cares if it is actually far less safe.......
     
  11. uOpt

    uOpt Gawd

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    Raid1 drives have a raid header and are not plain.

    However, systems like Linux md through grub will still be able to boot if you remove disks.
     
  12. MrGuvernment

    MrGuvernment [H]ard as it Gets

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    all raid levels write data to the drives to show they are in a raid array

    Point is, you can take a raid 1 drive OUT of a raid array and plug it into ANY other system and it will be accessible , and ALL of your files will be present and usable, assuming no damage to the drive occurred when the raid card died.
     
  13. Old Hippie

    Old Hippie [H]ardness Supreme

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    Sorry.....You are correct......I had RAID0 on my little mind. :)
     
  14. rigurat

    rigurat Limp Gawd

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    Thanks for the answers, I never knew a "raid header" until here.

    Other forums also point out that RAID 1 drives should should be readable on another PC but not always, some hardware raid cards write the RAID info on places that make drive unreadable outside the card.

    I plan on getting an LSI Megaraid card in the future.
     
    Last edited: Apr 18, 2015