Question about RAID 1

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RAID
RAID 1
I have a server with a RAID-1 array with 2 36 gig hard drives. I am wondering could I get another 2 hard drives and add them to the array, and then extend some already partitioned space without formatting?
ASKED: September 28, 2004  4:35 PM
UPDATED: May 24, 2012  2:29 PM

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If my memory serves me correctly, RAID-1 is just straightforward mirroring. Unfortunately you can’t do much with a mirror, other than replace RAID-1 with a larger drives to <a href=”http://www.partition-magic.org/hardware-raid/resize-raid-1-mirror-partition.html”>resize RAID 1 partition</a>. This is what I’d recommend, if your controller can handle it.

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  • Moonlite
    Depends if you're talking about controller based raid or host based raid. If you use host based raid, there is no extension possible. On most controller based raid arrays, a mirror can be migrated to raid 0+1 or raid 5 without losing data. I surely recommend you to not use host bases raid in a production environment. I've seen too much trouble when problems arise (performance gain is in many cases a minor issue). Regards.
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  • GregNottage
    I really don't think it's possible to migrate from a mirrored array to a striped array without formatting and starting over. If the original array was raid 0, then that's different as it's already in a stripe (albeit without parity). Please see Adaptec's article for more info: http://tinyurl.com/42knr Based on the original question, I don't believe you can migrate and keep the original data intact. Whatever you do, make sure you have a tested known good backup of the data before you try anything.
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  • JSilveira
    Remove the mirroring so only one drive is the system drive. Make two backups of the system drive(Two, incase one is bad. Just good practice.) Create your RAID 5 array. Restore the system backup to the new array.
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  • Moonlite
    Reviewing the former answers, adaptec appearently does not support Raid level migration on his controllers while Compaq/HP (and probably many other vendors) do support this for a long time. Review the quickspecs for e.g. de smartarray 6i controller at: http://h18004.www1.hp.com/products/quickspecs/12030_div/12030_div.html Regards,
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  • GregNottage
    OK, point taken. I see that it's possible with th 6i. I guess the question we should all be asking Natethegreat really is what server and make of raid card are you using? Then we can see if it's possible with the hardware you are using. On a side note though, have you tried doing one of these online migrations? I've heard many horror stories of people trying this in the past, and they've all ended up reverting to a data restore from tape. Natethegreat: make sure you heed the backup advice ;-)
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  • Dwiebesick
    You have not provided enough information to give you an accurate answer. However, if you are running out of space on your drives, and you are looking to just add free space, you could [depending on your operating system] make a second RAID 1 and use Microsoft's mount point technology to add free space. There are limitations to this that you need to consider. Check out MSKBA 812547. It really depends on what you are attempting to accomplish. If you have the choice, RAID 5 migration is what I recommnd. IF you chose to use RAID 5, I highly recommend staying with the same make and model of drives. If you have the drive bay space and adquate power, you can add as many drives to give you the space you need.
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  • Moonlite
    An alternative posibility when using controller based raid: Replace one disk with a model with more capacity. Have the controller rebuild the drive, then take out the second member and replace it as well. Have the controller rebuild it. Now you can perform a logical drive extension (supported on smartarray, starting with model 3200). When your OS is windows 2000 or windows 2003, you can use diskpart.exe (a microsoft resourcekit tool, free downloadable from their site) to extend the partition. I've used this method once in production environment. With the old disks, you can revert to the original situation whenever you want (the raid configuration metadata is written to disk as well as to the controller. Putting back an old disk does revert that particular array to the old situation)
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  • Howard2nd
    I concur with the preceding answers. RAID 0/1 Mirror cannot be extended without re-format. Since we do not how you implemented the RAID array (software/hardware), it is difficult to give an optimum answer. Your current available storage is 36GB and if you add equivalent drives in a second array you would get to 72GB available for 144 physical. If your SCSI card supports RAID 5 then 'BACKUP, Reformat, Install, Test, Restore' gives you a 104GB logical volume for the 144GB physical. Your decision is based on allowable downtime versus disaster recovery policies for your operation.
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  • Vibrunner
    http://www.techrepublic.com/forum/questions/101-237565/configure-raid-1-by-adding-second-drive
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