Technical data

Using BACKUP
11.15 Backing Up User Disks
the tape’s volume label with the label you specified and ensures that the tape
is expired.
If the tape is not expired or the label does not match, the command procedure
exits. If the tape is expired and the label matches, BACKUP writes the
expiration date you specified to the volume header record and initializes
the tape. After initializing the tape, BACKUP saves all files in the current
default directory tree that have been created or modified since the last save
operation to a save set with the name you specified.
11.15.8 Backing Up Volume Shadow Sets
Volume shadowing maintains multiple copies of the same data on two or more
disk volumes. If you use volume shadowing on your system, you can form a
shadow set by uniting individual disk volumes (shadow set members). Volume
shadowing duplicates data on each member of the shadow set. Per-disk licensing
is available for each disk you will be including in a shadow set. This option is
effective in a cluster where you intend to shadow only a small number of disks.
However, if you have larger systems with many more disks to shadow, traditional
capacity (per-CPU) licenses may be more appropriate.
Limits on the numbers of disks allowed in shadow sets are shown in Table 11–7.
Table 11–7 Number of Shadow Sets Supported
Type of Shadow Set Sets Supported
Single member Unlimited sets
Multimember Total of 400 disks in two- and three-member sets, or both
These limits apply per cluster. For example, 400 total disks could be configured
into 200 two-member shadow sets or into 133 three-member shadow sets per
cluster. If single, two-member, and three-member shadow sets are all present on
a single cluster, then a maximum of 400 disks may be contained in the two- and
three-member shadow sets.
You can use the firmware implementation of RAID level 1 (shadowing) to create
shadow sets using the SCSI (Small Computer Systems Interface) disks attached
locally to a single SWXCR-xx controller. The StorageWorks RAID Array 210
Subsystem (SWXCR-EA or SWXCR-EB EISA Backplane RAID controllers) and
the StorageWorks PCI Backplane RAID controller (SWXCR-PA or SWXCR-PB)
have their own firmware implementations of RAID, levels 0, 1, and 5.
SCSI disks connected to these controllers can also be included in shadow sets
created using host-based volume shadowing for OpenVMS. For example, with
host-based volume shadowing, you can create a RAID1 shadow set containing two
like disks, each of which is attached to a separate SWXCR-xx RAID controller
located within a cluster. SCSI disks can be configured as shadow sets when
attached to systems running volume shadowing for OpenVMS.
For directly connected SCSI devices that have been powered down or do not
answer to polling, the elapsed time before a device is removed from a shadow
set approaches one minute. In all other situations, the elapsed time closely
approximates the number of seconds specified in the SHADOW_MBR_TMO
parameter.
Using BACKUP 11–43