VERITAS Volume Manager 3.5 Migration Guide (August 2002)

Chapter 1, VxVM and LVM

Final 24 July 2002 Introducing the VERITAS Volume Manager

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)

combine the beneﬁtsof stripingto improve performance by spreading data across

multiple disks, and mirroring to provide redundancy of data. Striped mirror

volumes are more tolerant of disk failure and have a shorter recovery time than

mirroredstripevolumes. Refer tothe VERITASVolume Manager 3.5Administrator’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 andrelocatesthe affected subdisks. Thevxunrelocutility can beused 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-5toa mirroredlayout 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.

Note For more information on LVM, refer to HP-UX Managing Systems and Workgroups,

and LVM manual pages in HP-UX Reference Volumes 2, 3, and 5. For information on

VxVM commands, refer to the VERITAS Volume Manager documentation.