Introducing the VERITAS Volume Manager

Concatenation, the combining of discontiguous disk regions into virtual devices.

Spanning, concatenation across different physical media.

Striping, distribution of storage mappings for a virtual device so that multi-threaded accesses tend to cause even use of all physical media.

The VERITAS Volume Manager Storage Administrator vmsa, a JAVA-based GUI for VxVM. The Storage Administrator runs either as an application or from a web browser.

Dynamic Multipathing (DMP) for active-passive devices, such as Model FC30 and FC60. DMP provides higher availability to data on disks with multiple host-to-device pathways by providing a disk/device path failover mechanism. In the event of a loss of one connection to a disk, the system continues to access the data over the other available connections to the disk.

Free Space Management, providing simple goal-based allocation of storage.

Task Monitor, which tracks the progress of system recovery by monitoring task creation, maintenance, and completion. The Task Monitor allows you to pause, resume, and stop as desired to adjust the impact on system performance.

Dynamic Multipathing (DMP) for active-active devices, such as HP Surestore Disk Array xp256, HP Surestore Disk System FC10 and other disk devices. DMP provides higher availability to data on disks with multiple host-to-device pathways by providing a disk/device path failover mechanism. In the event of a loss of one connection to a disk, the system continues to access the data over the other available connections to the disk. DMP also provides in some cases, improved I/O performance from disks with multiple concurrently available pathways by balancing the I/O load uniformly across multiple I/O paths to the disk device. LVM supports path failover but does not support I/O balancing. DMP support may be used with devices that show improved performance when I/O is balanced across the multiple paths such as xp256, EMC Symmetrix disk array, and other OEM array devices.

Multiple mirroring with up to 32 mirror copies of a volume's address space.

Mirrored stripes (RAID-0 + RAID-1) and striped mirrors (RAID-1 + RAID-0).

VxVM supports the combination of mirroring and striping. When used together on the same volume, mirroring plus striping offers the benefits of spreading data across multiple disks (striping), while providing redundancy (mirroring) of data.

If in the near future you are planning on using this data in a clustered environment as a shared disk group, you should use mirrored stripes, because striped mirrors are not yet supported in a clustered environment. Otherwise, for non-clustered environments, use striped mirrors, since these offer a volume that is more tolerant of disk failure; if a disk failure occurs, the recovery time is shorter for striped mirrors. Refer to the VERITAS Volume Manager 3.1 Administrator's Guide for more detailed information on these layouts.

Hot-relocation, which allows a system to react automatically to I/O failures on redundant (mirrored or RAID-5) VxVM objects, restoring redundancy and access to those objects without administrative intervention. VxVM detects I/O failures on objects and relocates the affected subdisks. The vxunreloc utility can be used to restore the system to the same configuration that existed before the disk failure.

RAID-5, which provides data redundancy by using parity, at a lower storage cost than mirroring. RAID-5 provides data redundancy by using parity. Parity is a calculated value used to reconstruct data after a failure. While data is being written to a RAID-5 volume, parity is calculated by doing an exclusive OR (XOR) procedure on the data. The resulting parity is then written in an interleaved fashion to the RAID-5 array established by the volume. If a portion of a RAID-5 volume fails, the data that was on that portion of the failed volume can be recreated from the remaining data and parity information.

Online Data Migration, which allows for regions of storage on physical media to be dynamically moved to other physical devices.

Online Relayout or Dynamic Restriping, the ability to change logical data configuration while online, for example, to change RAID-5 to a mirrored layout or to change a stripe unit size. The volume data remains available during the relayout.

Improved RAID-5 subdisk, using layered volume technology where the RAID-5 subdisk move operation leaves the old subdisk in place while the new one is being synchronized, thus maintaining redundancy and resiliency to failures during the move.