Hold on a second. I think that you can add a larger disk to a raid group of smaller disks and the larger disk becomes the parity drive automatically. Then if you add more large disks, all the space on them is used.
I think the confusion here is a disk failure. If the hot spare is larger than the failed drive, then you waste space on the spare drive because only stripes from the failed drive are reconstructed on the spare. Extra space on the spare is not used.
So if you have a raid group with different size drives, its best to also have hot spares in those sizes. ONTAP is smart enough to replace a failed drive with a spare of the same size if possible. Otherwise it has to use a bigger replacement and that does indeed waste space.
Has this policy changed? If so, when?
Thanks Justin. So we can't change the parity disk from an 18gb disk to a 36gb disk kind of on the fly. We'd have to create a new volume and do a vol copy or some such thing. Not sure where we got the idea we could 'upgrade the parity disk'.
So we either have to buy 18gb shelves or re-architect our layout. (or waste half a disk adding a 36gb to an 18gb set but that's not a great option as our volume is growing quickly).
Yes, you're going to have a problem.. :(
If you add 36GB drives to an existing RAID group of 18GB disks, the 36GB disks will be reported and used as 18GB drives.
Once a RAID group is established with a parity drive of xxGB, any disks added to that RAID group will only be used to the same capacity (xxGB) as the parity drive.
If you reverse the situation, and add 18GB drives to an existing 36GB drive RAID group, all drives will be used to their full capacity, but you will run into performance troubles as the volume fills up and the system is forced to write only to the larger disks, thereby reducing the number of physical spindles working for you.
You will definitely want to create a new RAID group (or a new volume) for your 36GB drives to take advantage of the higher capacity.
Justin Sullivan Network Appliance, Technical Support Engineer Network Appliance Certified Associate justins@netapp.com Get answers NOW! - NetApp On the Web - http://now.netapp.com Tech Support Hotline: 1-888-4NETAPP
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