Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Figure 1-19
How the failure of a single disk affects mirrored-stripe and
striped-mirror volumes
Striped plex
Failure of disk detaches plex
Detached
striped plex
Mirror
Mirrored-stripe volume
with no
redundancy
Striped plex
Mirror
Striped-mirror volume
with partial
redundancy
Failure of disk removes redundancy from a mirror
When the disk is replaced, the entire plex must be brought up to date. Recovering
the entire plex can take a substantial amount of time. If a disk fails in a
striped-mirror layout, only the failing subdisk must be detached, and only that
portion of the volume loses redundancy. When the disk is replaced, only a portion
of the volume needs to be recovered. Additionally, a mirrored-stripe volume is
more vulnerable to being put out of use altogether should a second disk fail before
the first failed disk has been replaced, either manually or by hot-relocation.
Compared to mirrored-stripe volumes, striped-mirror volumes are more tolerant
of disk failure, and recovery time is shorter.
If the layered volume concatenates instead of striping the underlying mirrored
volumes, the volume is termed a concatenated-mirror volume.
RAID-5 (striping with parity)
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
Understanding Veritas Volume Manager
Volume layouts in VxVM
44