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The reported size of a SCSI drive, Fiber Channel disk or RAID LUN will be much smaller than the actual size of the disk. As a result, the full size of the disk may not be usable. This issue can occur in the following releases: x86 Platform, Solaris 7, Solaris 8, & Solaris 9. As a result the full size of the disk may not be usable.

What's happening is that on these systems the number of cylinders for a disk is stored as a 16-bit value. So on systems where accessing the entire disk requires more than 65535 cylinders only the lower 16-bits of the actual number of cylinders are used.

The following example shows how to determine if a disk is too large and may be impacted by this issue:

  # format
Searching for disks...done

  AVAILABLE DISK SELECTIONS:
0. c1t0d0 <DEFAULT cyl 61918 alt 2 hd 255 sec 63
/pci@1,0/pci8086,340f@7/sd@0,0                                    

This disk is 2047598591 sectors in size, which was determined using the disk_size utility which is shown in Bug ID: 5042195, (The only argument required by the disk_size utility is the path to the disk needs to be checked. This utility will show the actual disk capacity as it is reported to Solaris).
You can estimate the capacity in sectors by taking the size in megabytes and multiplying it by 2048.

In this case the cylinder size is 16065 (255 x 63 = 16065).
Therefore, the number of cylinders for this disk should be:

  2047598591 divided by 16065                                    

This works out to be 127457.12 (expect this to almost always end up as a fractional cylinder value), which is well over 65535.
When converting to hex you get:

  1F1E1                                    

At this point you can see that it is likely that the disk will be affected by this issue due to the hexedecimal value being greater than 4 digits.

Further confirmation that a system is experiencing this issue can be obtained by converting only the lower four hex digits back into decimal which yields 61921. Adding the alternate cylinders shown by format (alt) to the cylinders shown by format (cyl) gives us 61920, which is close enough to show that the described issue is being experienced.
Also keep in mind that you will be using an estimate of the true disk size, so it is expected the result will be off by a few cylinders.
If this occurs a large portion of the disk will be unusable and no errors will be seen from fdisk or format.

This issue has been occurring when mirroring two internal 72GB drives in the V20z/40z systems. The work around is to create a legal Solaris fdisk and volume table of contents (VTOC) prior to mirroring the disks. This will ensure a good geometry is applied to the VTOC on the disk. After the VTOC is present on the disk you can then be mirror the two disks and the geometry values in the VTOC will be used in instead of those in the disk reports.

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