Reconfiguring raid 5 confirmation

phoeneous

Say a server has 7 disks. Disks 0 and 1 make up a raid 1 array which holds the os. Disks 2-6 make up a raid 5 array which just holds data. Is it possible to remove disks 5 and 6 from the raid 5 array without losing data? Ideally I'd like to create a new raid 1 array with disks 5 and 6 only.

undomiel

Well I haven't seen a raid controller that allows removing disks. To do that you have to delete and recreate the RAID. You'll want to calculate that you still have enough space for the data after doing that for instance if the disks are 300 GB disks and you recreate the RAID5 with 2 less then you'll be losing 600 GB from that array. That's a fair chunk of space there. So if you're still ok then you'll need to back up the data, delete and recreate the array with the correct number of disks, then restore the data onto the new array. That will leave you your disks for the new RAID1.

phoeneous

undomiel wrote: »

Well I haven't seen a raid controller that allows removing disks. To do that you have to delete and recreate the RAID. You'll want to calculate that you still have enough space for the data after doing that for instance if the disks are 300 GB disks and you recreate the RAID5 with 2 less then you'll be losing 600 GB from that array. That's a fair chunk of space there. So if you're still ok then you'll need to back up the data, delete and recreate the array with the correct number of disks, then restore the data onto the new array. That will leave you your disks for the new RAID1.

Yeah, I had a feeling I'd have to delete the array and create two new ones. I've confirmed that I will have enough space when going from 5 disks to three.

sratakhin

You can only remove one disk from a RAID 5 array and even that is not recommended. As soon as you reinsert the disk, the RAID controller will start recalculating parity, even if it's the same disk you removed.
Backup all data and start from scratch. Or just buy a few hard drives.

Paperlantern

Yeah RAID 5 can only sustain one disk loss before the array is lost completely. To confirm really what's been said above, the only way to reconfigure disk members in RAID 5 is to back up the data, verify it is a good backup, then break the array and reconfigure the disks as desired. RAID levels are great for redundancy, but unless it is a robust system (like an advanced NAS device with its own RAID-like storage system, for example, a Drobo), it is impossible to adjust the size of a already created array.

The best Ive ever been able to do is replace all disks is a RAID 5 array with disks that were twice the size, once the final one rebuilt and the array was healthy again, I was able to create another volume with the unused space on all the disks, but of course was not able to do anything with the existing volume that was in place.