For disk groups that support the Cross-platform Data Sharing (CDS) feature, the upper limit on the minor number range is restricted on AIX, HP-UX, Linux (with a 2.6 or later kernel) and Solaris to 65,535 to ensure portability between these operating systems.
On a Linux platform with a pre-2.6 kernel, the number of minor numbers per major number is limited to 256 with a base of 0. This has the effect of limiting the number of volumes and disks that can be supported system-wide to a smaller value than is allowed on other operating system platforms. The number of disks that are supported by a pre-2.6 Linux kernel is typically limited to a few hundred. With the extended major numbering scheme that was implemented in VxVM 4.0 on Linux, a maximum of 4079 volumes could be configured, provided that a contiguous block of 15 extended major numbers was available.
VxVM 4.1 and later releases run on a 2.6 version Linux kernel, which increases the number of minor devices that are configurable from 256 to 65,536 per major device number. This allows a large number of volumes and disk devices to be configured on a system. The theoretical limit on the number of DMP and volume devices that can be configured on such a system are 65,536 and 1,048,576 respectively. However, in practice, the number of VxVM devices that can be configured in a single disk group is limited by the size of the private region.
When a CDS-compatible disk group is imported on a Linux system with a pre-2.6 kernel, VxVM attempts to reassign the minor numbers of the volumes, and fails if this is not possible.
To help ensure that a CDS-compatible disk group is portable between operating systems, including Linux with a pre-2.6 kernel, use the following command to set the maxdev attribute on the disk group:
# vxdg -g diskgroup set maxdev=4079
You can use the following command to discover the maximum number of volumes that are supported by VxVM on a Linux host:
# cat /proc/sys/vxvm/vxio/vol_max_volumes 4079
See the vxdg(1M) manual page.