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adding drives to a RAID 5 array

Posted on 2004-10-02
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How easy is it to add drives to a RAID 5 array?

i'm getting an external IBM EXP400 DAS SCSI storage enclosure that supports up to 14 disks.  I'm starting with 4 300 GB disks and will scale up when i need more storage.

I think its pretty easy to add RAID 1 disks to this - i just add another two and configure them.

what about RAID 5?  as i understand it, in RAID 5 all disks depend on each other... so how do you add new disks?  do you have to take down the array and then add the disks and bring it back up again?  Is there any way to do it on the fly by adding hot-swappable disks?
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Question by:kenshaw
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andyalder earned 750 total points
ID: 12206750
It depends whether you hang your SCSI enclosure off a RAID controller or a simple SCSI controller. If you have a non-RAID controller and create the array in software to add a disk you have to wipe it out and build another array encorporating the extra disk. If you have a RAID controller on the other hand you just put another drive in the box and in the config utility tell it to expand the array on the fly. It slows down a bit while expanding so it's best to do it overnight. This won't give you a bigger partition under the OS of course but (assuming windows) you can use diskpart.exe to expand the partition and increase the volume size. Sometimes diskpart expands the partition but doesn't complete increasing the volume size, if that happens then phone MS PSS and they have a free utility to finish off increasing the volume size.

If using a RAID controller be very wary about expanding the volume if you have dynamic disks, it can lead to data loss. Never had a problem with basic disks though.
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Whenever I've done a true RAID 5 on boxes, to add an additional single disk I either had to copy off the data and recreate the array with the new disk and then copy the data back or add the new disk as a mount point.  Basically a folder on the Raid5 array would point to the new disk or disk array that you have created.  Some of the controllers I've used don't permit expanding a Raid5 array on the fly and for myself, the best option for me was always to copy off the data, recreate the new array and copy the data back.

Steve
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by:x86fix
ID: 12214519
If you are using a raid controller it is generally very easy to increase the size.  You just install the new drives and then add them to the Raid.  Many controllers auto detect and auto add them.
If the box allows hot swaps, even easier.
Depends mostly on the controller and the software it uses.
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