I'm interested in learning more about NetApp "Right Sizing" of drives, with the hope of recovering more usable capacity. For example let's take a brand-new FAS2020 with 1TB Drives:
The drives report out as X298_SMOOS01TSSS, which maps to IBM part number 45E2141. The actual drive appears to be a Seagate Barracuda ES.2 Model ST31000640SS (or ST31000640SS for SAS). The vendor specifications for that drive ( Barracuda ES.2 SATA Product Manual ) show "guaranteed sectors" of 1,953,525,168. Reformat that from 512 bytes/sector to 520 and you should have 1,923,470,934 raw usable sectors, at a very minimum, accounting for all drive overhead and all drive remapping spares.
Yet the actual filer reports a significant NetApp tax:
RAID Disk Device HA SHELF BAY CHAN Type RPM Used (MB/blks) Phys (MB/blks)
--------- ------ -- ----- --- ---- ---- ---- -------------- --------------
dparity 0c.00.1 0c 0 1 SA:B SATA 7200 847555/1735794176 847884/1736466816
parity 0c.00.4 0c 0 4 SA:B SATA 7200 847555/1735794176 847884/1736466816
Which is line with the loss predicted at: http://communities.netapp.com/servlet/JiveServlet/download/21878-11275/Right-sized%20disks.pdf ("Right-sized Disk Capacity").
So we lost basically 10% before we even began the loud bickering between storage vendors.
Now the official reason for all this is found direct from NetApp:
"Disk drives from different manufacturers may differ slightly in size even though they belong to the same size category. Right sizing ensures that disks are compatible regardless of manufacturer. Data ONTAP right sizes disks to compensate for different manufacturers producing different raw-sized disks."
But this seems like nonsense for several reasons. First, every vendor will produce 1TB drives with at least 1,000,000,000 raw usable bytes, because otherwise they can't sell them as 1TB drives. So we ought to get at least that much. Second, NetApp should have enough market power to insist that each Barracuda sent to NetApp have a certain minimum number of actual sectors (Seagate can sell the slightly smaller ones as desktop drives via some bottom feeding low price vendor). We're paying enough premium for the drives, someone else should adsorb the cost of drive size varriance. And Third, I fully expect to be able to get Barracuda drives on eBay well into the next millenium. I'm not swapping out the rest of my drives, I'll always buy a similar one, so I don't care about supporting multiple vendors.
So I'm curious if there is a way to trick OnTAP into using more sectors. On a 12 drive filer with RAID-DP, that's well over 1 Terrabyte of missing usable storage space.
