Need help deciphering Operations Manager display

Hi all.

I have been trying to determine what the various stats I get out of Operations Manger mean.  I have read access to the web based Operations manager, this version:

About NetApp® Operations Manager
19 Sep 10:42
Operations Manager is the web interface of the DataFabric® Manager server. It is used for day-to-day storage management activities.
About DataFabric® Manager server
Version 4.0.2 (4.0.2)

I've been searching both these forums and for some of the terms used in the Operations Manager display, and not finding much.  I think in some instances, perhaps Op Mgr uses different terminology than what's used in most of the documentation and by users in this community.

(Some specifics here, actual questions at the bottom)

For example, I have a 1 Tb chunk of disk on an aggregate. Our Netapp admin refers to this as a volume. In Op Mgr, the volume is listed as 900 Gb with 100 Gb Snapshot reserve.  The entire 1Tb is presumably a "file system" as it is listed on the File System page, Member Details tab, under "Volume Details" in Op Mgr.

This space is used to provide LUNs for a Win 2008 R2 file server. They were configured and snapshots are created using Snapdrive 6.1, which is my main administration tool.

There are a  total of 400 Gb allocated to three LUNs, Windows reports that about 104 Gb of this is actually used.

Here's the piece of the Op Mgr display I'm writing about:

Volume Size and Snapshot Reserve Size I  understand. 

I can also see that Available Snapshot Reserve and Used Snapshot Space add up to the Snapshot Reserve Size.

Space Reserved Data makes sense too (the sum of the three LUNs)

Unused Guaranteed Space makes sense too, if you allow for rounding and a bit of fudge in the way Windows calculates used disk space.    104 Gb used space in Windows + 11.8 Gb of snapshots + 881 Gb unused guaranteed space = 996.8 Gb, fairly close to the total "file system" size.

The phrase "fractional overwrite percent" cannot be found at, though I suspect it is the same as "fractional reserve".


"Available Reserve for Data Writes" can't be found at either.   How is that calculated?  I can't see where the 107 Gb comes from.

Same question about the Unsed Space.  I can't see how any combo of the nubmers reported by Op Mgr and the actual used spce of 104 Gb result in 392 Gb.

Any help would be greatly appreciated.

Need help deciphering Operations Manager display


Aggregate, Volume, LUN relationships can get a little confusing. If you have a 1 TB volume with 10% reserved for Snapshots, that leaves you with 900 GB usable for data on that volume. Keep in mind, the Snapshots can actually consume more than the 100 GB guaranteed begin to consume more of the volume. I think you have that part.

Now with the LUNs. Basically ignore what Windows is reporting as used when trying to figure out how much space of your volume is being consumed. In your picture you see Space Guarantee is at the volume level. When setting up a LUN you can also guarantee space or thin provision. So if you set up three 133 GB LUNs that were space reserved, as soon as these are created they consume 399 GB of the available volume space. If the LUNs are thin provisioned (no space guarantee) they will only consume volume space as data is written to the LUN. Furthermore, when setting up the LUN through SnapDrive, you have the option to reserve space for at least one Snapshot. This is in addition to the volume level Snapshot reserve. So, if you have a 400 GB LUN, it would reserve an additional 400 GB to make sure at least one Snapshot of the LUN could occur. 400 GB LUN + 400 GB LUN Snap reserve + 100 GB Volume Snap reserve +107 GB available for writes would equal your 1 TB volume.

Hope I have my facts completely straight and it helps somewhat.


Need help deciphering Operations Manager display

Thanks Wes. 

Your explanation is essentially how I understood things to work, and it helps to get reinforcement that I at least have a basic grasp.  A couple of the stats still puzzle me:

How is the “Available reserve for data writes  107Gb”  calculated?

How is “Unused space 392Gb”  (as opposed to “Unused Guaranteed space.”) calculated? 

Even a definition of those specifc terms would be helpful.

Thanks again,