HP XP Business Copy Software - Manual (Page 33)

Every volume can have up to three Mirror Unit (MU) numbers associated with it. The MU number
designates a pair for which the volume is a member. The MU number is not the number of the pair,
but the number of the volume. A pair is made up of two volumes of which each pair member could
have the same or different MU numbers.
• MU=0 is the number of a volume for its first pair.
• MU=1 is the number of the same volume for its next pair.
• MU=2 is the number of the same volume for its third pair.
• The MU number of an S-VOL is always MU=0.
For Level 1 (L1) pairs, the root volume could have MU=0, MU=1, and MU=2. For L1 pairs, the
associated S-VOLs all have MU=0 because this is the first pair of which they are a member.
For the Level 2 (L2) pairs, the L1 S-VOLs are now all acting as L2 P-VOLs. Because they are already
a member of one pair, the next MU number for each of them is MU=1 for their first L2 pair and MU=2
for their second L2 pair. For the S-VOLs associated with each of these pairs, the MU number is once
again MU=0 because this is the first pair of which they are a member.
Figure 12 Cascade pairs
.
When L1 and L2 cascade pairs are created, the P-VOLs and S-VOLs of the cascade pairs are classified
using the following terms (as shown in the previous figure):
XP Business Copy User Guide 33