Filter
Top Products
Figure 1 BC overview
Use BC from the Command View XP management station or XP Remote Web Console to make local
copies of volumes. The volume that has original data is called a P-VOL (primary volume), and a volume
to which data is copied is called an S-VOL (secondary volume). Pairs of P-VOLs and S-VOLs made by BC
are called BC pairs. You can specify an S-VOL as a P-VOL to make another two BC pairs. As a result,
you can use BC to make a total of nine S-VOLs. Use the cascade style to make BC pairs by specifying
S-VOLs as P-VOLs. In cascade style, pairs in the first cascade layer are called L1 pairs and pairs in
the second cascade layer are called L2 pairs.
BC volume pairs (P-VOLs and S-VOLs)
Disk arrays contain and manage original and copied BC data. The XP1024/XP128 disk arrays support a
maximum of 8,190 BC volumes: 4,095 pairs and the RAID Manager command device. The XP12000
disk array supports a maximum of 16,382 BC volumes (8,191 pairs: (8,191 P-VOLs and 8,191 S-VOLs) and
the RAID Manager command device. When BC pairs include size-expanded LUs, the maximum number
of pairs decreases. When pairs include more than one S-VOL, the maximum number of P-VOLs decreases.
BC performs copy operations for logical volume pairs that you establish. Each BC pair consists of one
primary volume (P-VOL) and up to three secondary volumes (S-VOLs). These volumes can be located
in the XP disk array or in external storage attached to the XP disk array. BC S-VOLs are secondary or
mirrored volumes containing backup data. Each S-VOL must be paired with only one P-VOL. During BC
operations, P-VOLs remain available to all hosts for read and write I/O operations (except during reverse
resync and quick restore). S-VOLs become available for host access only after the pair is split.
When a BC volume pair is created, data on the P-VOL is copied to the S-VOL to synchronize the volumes.
During this initial copy operation and after the pair is synchronized, all write operations to the S-VOL are
prohibited. To access an S-VOL, you can “split” the pair to make the S-VOL accessible. While a BC pair
is split, the disk array keeps track of all changes to the P-VOL and S-VOL. When you “resync” the pair, the
12
Business Copy XP (BC) for the Array