A Netapp support engineer just told me I could double the size of an aggr by replacing all its 1/2 TB disks with 1 TB disks, without destroying and rebuilding the aggr.
This might be feasible for us since we have an aggr that started out years ago as all-1/2 TB disks, and over the years Netapp has shipped 1/2 TB disks to us to replace 1/2 TB disks that have died, and/or people have bought 1TB disks and mixed them into the aggregate. The aggr is now about 2/3 1 TB disks, of course the 1TB disks are all downsized to 1/2 TB.
The Netapp engineer says that if we: First step - upgrade all the parity disks to 1 TB, and Second - upgrade all the rest of the disks in the aggr to 1TB, the aggr will start using the full size of the disks and essentially the size of the aggr will (magically!) double.
It might not work in our case - the aggr is already 46 TB with the disks at 1/2 capacity, and there is a 75 TB limit on aggr size on our filer (FAS3140/Ontap 8.1.2).
Considering the cost, it only makes sense in a few cases, like when aggrs are fairly small and most of the disks have been upgraded by disk failures over the years.
The other caveat is that we were told it works only for the entire aggr, not just one raid group at a time.
Thanks, all. FWIW, we do have some raid groups where the 1/2 TB "dparity" disk failed, as well as some others, and the dparity disk was then *not* downsized. The "dparity" disk was not downsized, and the "parity" disk was:
RAID group /aggr1/plex0/rg2 (normal, block checksums)
RAID Disk Device HA SHELF BAY CHAN Pool Type RPM Used (MB/blks) Phys (MB/blks) --------- ------ ------------- ---- ---- ---- ----- -------------- -------------- dparity 1a.11.20 1a 11 20 SA:A - BSAS 7200 847555/1735794176 847884/1736466816 parity 1a.11.18 1a 11 18 SA:A - BSAS 7200 423111/866531584 847884/1736466816 data 1a.11.0 1a 11 0 SA:A - BSAS 7200 423111/866531584 847884/1736466816 data 1c.02.19 1c 2 19 SA:B - BSAS 7200 423111/866531584 423946/868242816 [etc - mix of 1/2 and 1 TB disks]