Xsan 1.3
Xsan 1.3 supports LUNs larger than 2 TB. Xsan 1.3 is a downloadable update recommended for all Xsan users.
Xsan 1.0 to 1.2
Xsan 1.2 and earlier supports LUN sizes of 2 TB (terabytes) or smaller. However, if you're using an Xserve RAID that provides LUNs larger than 2 TB (such as Xserve RAID installations that use the newer 500 GB hard drives), you can use RAID Admin to create RAID sets that are smaller than 2 TB, or use the slicing feature in RAID Admin (under the Advanced tab) to divide existing RAID sets into smaller LUNs. Please keep this in mind when planning your Xsan network setup.
For optimal performance, use the following procedure as your guideline.
Step 1: Minimize the number of slices
In RAID Admin, slice the available storage into as few slices as possible, making sure to keep each below 2 TB. For example, create 2 LUNs from one that is initially 3.5 TB.
In the diagram below, the 3.5 TB LUN that comprises the drives on the left side of the Xserve RAID (controlled by the upper controller) has been sliced into two LUNs (LUN0, LUN1), while the 3.5 TB LUN that comprises the drives on the right side of the Xserve RAID (controlled by the lower controller) has also been sliced into two LUNs (LUN0, LUN1).
After you finish slicing, restart all Xsan nodes so that they recognize the slices.
Step 2: Correlate LUNs to RAID slices
Next, determine which LUNs in Xsan Admin correspond to which RAID slices. Open RAID Admin, click the Fibre Channel tab, and note the World Wide Name (WWN) for both the upper and lower controllers.
Choose Setup > LUNs. Each new slice should appear as "Unlabeled." The Information panel for each LUN includes a LUN number and a WWN that will correspond with the WWN of one of your Xserve RAID controllers.
In our example, the WWN 50:00:39:30:00:00:9A:44:0 corresponds to the Xserve RAID's upper controller, WWN 60:00:39:30:00:00:9A:44:0, and this LUN has the LUN ID 0.
Tip: It's a good idea to label each LUN according to its physical position in the rack and within the RAID. For example, we labeled a LUN with the LUN ID 0 that's associated with the upper controller of the second Xserve RAID in our rack as RAID2LeftLUN0.
Step 3: Create the Xsan volume
In Xsan Admin, choose Settings > Storage. When creating an Xsan volume that uses slices for LUNs, be sure to choose Fill from the Allocation Strategy pop-up menu for your storage pools.
Step 4: Add the slices to a storage pool
As you add LUNS (in this case, slices) to storage pools, limit yourself to one slice per RAID controller per storage pool. For example, if you create a new volume, MyVol, and three storage pools—MetaPool, FastPool, and FasterPool—you could add them like this:
Note that both FasterPool and FastPool contain one slice from each side of your Xserve RAID. Since we set the Allocation Strategy for FasterPool to Fill, it will fill up before FastPool is written. Slices with lower LUN IDs will be slightly faster than those with higher LUN IDs. In our example, the LUN ID 0 slices belong to FasterPool, while the LUN ID 1 slices belong to FastPool.
If you add LUNs, which are slices of a pre-existing Xsan volume, you should create new storage pools to handle the new storage, and change the volume's Allocation Strategy to Fill.