Veritas 4.1 Installation Guide (HP-UX 11i v3, February 2007)

Non-Layered
In a non-layered volume layout, a subdisk maps directly to a VM disk. This allows the subdisk
to define a contiguous extent of storage space backed by the public region of a VM disk.
Layered Volumes
A layered volume is constructed by mapping its subdisks to underlying volumes. The subdisks
in the underlying volumes must map to VM disks, and hence to the attached physical storage.
VxVM Storage Layouts
Data in virtual objects is organized to create volumes by using the following layouts:
• Concatenation and Spanning
• Striping (RAID-0)
• Mirroring (RAID-1)
• Striping Plus Mirroring (Mirrored-Stripe or RAID-0+1)
• Mirroring Plus Striping (Striped-Mirror, RAID-1+0 or RAID-10)
• RAID-5 (Striping with Parity)
Concatenation and Spanning
Concatenation maps data in a linear manner onto one or more subdisks in a plex. To access the
data in a concatenated plex sequentially, data is first accessed from the first subdisk from
beginning to end and then accessed in the remaining subdisks sequentially from beginning to
end, until the end of the last subdisk.
Striping (RAID-0)
Striping maps data so that the data is interleaved among two or more physical disks. A striped
plex contains two or more subdisks, spread out over two or more physical disks.
Mirroring (RAID-1)
Mirroring uses multiple mirrors (plexes) to duplicate the information contained in a volume. In
the event of a physical disk failure, the plex on the failed disk becomes unavailable.
When striping or spanning across a large number of disks, failure of any one of the disks can
make the entire plex unusable. As disks can fail, you must consider mirroring to improve the
reliability (and availability) of a striped or spanned volume.
Striping Plus Mirroring (Mirrored-Stripe or RAID-0+1)
VxVM supports combination of mirroring above striping. The combined layout is called
mirrored-stripe layout. A mirrored-stripe layout offers the dual benefits of striping to spread
data across multiple disks, while mirroring provides redundancy of data.
Mirroring Plus Striping (Striped-Mirror, RAID-1+0 or RAID-10)
VxVM supports the combination of striping above mirroring. This combined layout is called a
striped-mirror layout. Putting mirroring below striping, mirrors each column of the stripe. If
there are multiple subdisks per column, each subdisk can be mirrored individually instead of
each column.
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 volume is reflected in all copies. If a portion
of the 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,
16 Product Overview