It looks like a mistake was made when the volume was created. The screenshot shows one affinity tag with 3 LUNs under it. By the size of the affinity tag, it seems all 3 LUNs are in one storage pool and that the two 9 TB LUNs are only being used as 749.99 GB LUNs. (3 x 749.99 GB = 2249.97 GB = 2.25 TB)
Is the actual size of the volume when mounted on an Xsan client 2.25 TB?
Sorry for suggesting a mistake was made in the initial configuration. It actually looks like Xsan Admin is showing incorrect info in the expansion dialog box. Here are a few things to try:
1. Check that each MDC has the same contents in the XSAN1FS.cfg and XSAN1FS-auxdata.plist files in /Library/Filesystems/Xsan/config. If they do, could you paste the contents of both files here?
2. Try closing the window in Xsan Admin and clicking "disconnect". Then go to File -> New -> Connect to existing SAN and reconnect to your MDC. (Alternatively, use Xsan Admin from a different Mac or a different user account.) Then bring up the expansion dialog again. Does it still look the same?
3. Reboot each MDC and then bring up the expansion dialog again.
4. Edit the volume config file manually and use cvupdatefs to expand the volume. I'm just mentioning this as a potential option. I do not recommend doing this unless you really know what you're doing.
5. Contact Apple Xsan support.
Please read the Xsan guidelines for volume expansion, specifically the part about storage vs bandwidth expansion (excerpted below)
A “storage expansion” occurs when LUNs are added to newly created storage pools. When adding capacity to an Xsan volume is the goal, consider storage expansion first.
A “bandwidth expansion” occurs when you add LUNs to existing storage pools. A bandwidth expansion should be considered when the primary goal is to improve the bandwidth of a storage pool. Avoid bandwidth expansions if your goal is only to increase capacity.
Did you use the Xsan 2 setup assistant? What kind of XSAN did you specify? Video or file server, etc How many LUNs did it ask for in each storage pool, 2 or 4?
If I was really pressed for time, or just wanted sotrage expansion, then I would create a new storage pool and add the two new LUNs.
If I had the time I would back it up, blow it away and create one new storage pool with four LUNs. That would be right for video, but maybe this is not a video workflow based SAN.
What is it used for?