VERITAS Volume Manager 4.1 Administrator's Guide

Understanding VERITAS Volume Manager

Volume Layouts in VxVM

Chapter 130

NOTE The VERITAS Enterprise Administrator (VEA) terms a striped-mirror

as Striped-Pro, and a concatenated-mirror as Concatenated-Pro.

RAID-5 (Striping with Parity)

NOTE VxVM supports RAID-5 for private disk groups, but not for shareable

disk groups in a cluster environment.

NOTE You may need an additional license to use this feature.

Although both mirroring (RAID-1) and RAID-5 provide redundancy of

data, they use different methods. Mirroring provides data redundancy by

maintaining multiple complete copies of the data in a volume. Data being

written to a mirrored volume is reﬂected in all copies. If a portion of a

mirrored volume fails, the system continues to use the other copies of the

data.

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 to the

volume. The data and calculated parity are contained in a plex that is

“striped” across multiple disks. 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. It is also possible to mix

concatenation and striping in the layout.

The ﬁgure, “Parity Locations in a RAID-5 Model,”, shows parity locations

in a RAID-5 array conﬁguration. Every stripe has a column containing a

parity stripe unit and columns containing data. The parity is spread over