In vSphere, the next version of ESX server, VMware had included the new features, which provide capability to rename the device’s name for each of the LUN been presented to the ESX hosts. This will provide alternative to keep track the physical LUNs which presented to ESX hosts and VMs too.

This show the device name had been modified to match with my datastore name. If you do assigned it to a virtual machine, you can easily rename it to the virtual machine name as you need.

Now the device name shown same as the datastore name. If you assign the LUNs to be a RDM on virtual machine, it will not able to be displayed on this screen. The only way to keep track is on the last screen shot which show the physical path which connected to the LUNs.

Article Copy from VMware

In Multipathing Configurations the Number of Paths Per LUN Is Inconsistent
The hpsa driver in ESX Server might reduce the number of supportable LUNs below the expected maximum limit of 256 when the controller is used in multipath configurations. In multipath configurations, if all four paths are configured, the total supportable LUNs is reduced to 64. In certain multipath configurations, because each target path consumes an available LUN slot, the total number of supportable LUNs might be reduced to 60.

Workaround
Reduce the number of LUNs on a server until the product of LUNs and paths is less than 256 (LUNs * Number of paths < 256), and if necessary, reduce the LUN count depending on use of multipath until each LUN has the expected number of paths.
The following example shows a configuration with the maximum supportable LUNs presented to an ESX Server installation on four paths, providing all LUNs with the expected number of usable paths:
Path 1: 63 LUNs seen through this path; Total LUN count (63 + 1 path) is less than 256
Path 2: 63 LUNs seen through this path; Total LUN count (63 + 63 + 2 paths) is less than 256
Path 3: 63 LUNs seen through this path; Total LUN count (63 + 63 + 63 + 3 paths) is less than 256
Path 4: 63 LUNs seen through this path; Total LUN count (63 + 63 + 63 + 63 + 4 paths) = 256

If I do use the formula above to calculate my environment, yes, I am at the full limit of 256 LUNs. I have 2 ESX servers which only have 2 HBA connection, and had no problem to present more than 67 physical LUNs to it until now. What I had done now is, I removed 2 HBA connection from each of my ESX servers, and run the rescan, and I found that the LUN is presented as I expected. Again, I am not confirmed with the solution yet and will do another round confirmation with the VMware engineer on this.

Have a look here:
VMware ESX VMFS LUNs Report.

I would suggest you try snackcheck and smtp_send.pl scripts provided by YellowBricks.

Sending snapcheck html email from the service console
# /usr/local/bin/smtp_send.pl -t toyouremail@malaysiavm.com -s ” `hostname` Diskspace report of the VMFS volumes” -f fromemailadd@malaysiavm.com -m “`cat /var/log/vdf.html`” -r SMTPserver

Our design for a storage on ESX is 300GB, allow maximum VMFS up to 256GB.

The reasons behind are:

• better I/O performance: Each storage in ESX, we only assign to 5 VMs or less. Since more running VMs on a single storage will hit into the LUN I/O speed bottle neck.
• better disk utilization: You can safe lots of unuse space when you do it small. Say You assign a 2TB storage that can keep 40 VMs, but you only have 20 now, you actually waste 1TB which is sitting there doing nothing. But if you make each storage small, you can create only when you need it. It is much more manageable on SAN disk allocation point of view.

You may ask, if we need a disk in VM that is larger then 256GB? Well, up to that size, you need to consider I/O performance as well, VMFS is just not capable for that size if you are looking for performance as well. Normally we assign a RAW Device for that, you can connect a RAW up to maximum 2TB disk space if required. Check VMware VMFS vs RDM.

The most important point to fasten up LUNs speed is increase the spindle count on your LUN. And this can be achieve by Meta up few Single LUNs.

If you have 3 RAID Groups with 7 + 1 RAID 5 Configuration (7 Disks join as a RAID 5 Group and 1 as Hot spare), and you create a 60GB Single LUN on Group 1, you have 7 spindles to run this LUN. But if you create 20GN Single LUNs on each of your RAID Groups and Meta Stripe them together to become a 60GB Meta LUN, you are having 3 X 7 = 21 Spindles to run this LUN (theoretically we should call this RAID as RAID 50).

The same setting can apply to RAID 10 LUNs too, it will then become RAID 100.

Note:

• To create Meta Stripe LUN, you need to have Single LUNs with same size and same RAID type.
• Meta Strip and Meta Concatenation is difference. Meta Concatenation DO NOT improve performance!