For VxVM versions prior to 5.1SP1, the CDS (Cross-Platform Data Sharing) implementation is based on the Solaris sparc VTOC (also referred to as the Volume Table Of Contents) disk labeling scheme and the Solaris VTOC disk label does not support physical disks greater than 1 terabyte. CDS disk label depicts the details of disk geometry (the disk geometry consists of number of cylinders, heads, sectors and size of the sector, and product of these values gives the disk capacity). The disk geometry and capacity can also be obtained through SCSI mode sense commands and in general, values obtained through these two methods should match.

The following is a description of the problem according to the Etrack incident listed in the Supplemental Materials section of this article.

DESCRIPTION:
The CDS disk maintains a SUN vtoc in the zeroth block of the disk. This VTOC maintains the disk geometry information like number of cylinders, tracks and sectors per track. These values are limited by a maximum of 65535 by design of SUN's vtoc, which limits the disk capacity to 1TB. As per SUN's requirement, few backup VTOC labels have to be maintained on the last track of the disk.

VxVM 5.0 MP3 RP3 allows to setup CDS disk on a disk with capacity more than 1TB. The data region of the CDS disk would span more than 1TB utilizing all the accessible cylinders of the disk. As mentioned above, the VTOC labels would be written at zeroth block and on the last track considering the disk capacity as 1TB. The backup labels would fall in to the data region of the CDS disk causing the data corruption.

RESOLUTION:
Suppress writing the backup labels to prevent the data corruption.