Volume Pairs - Hitachi AMS 2000 User Manual

• Interface and command software, used to perform TCE operations.
Command software uses a command device (volume) to communicate
with the arrays.
Figure 1-1
•

Volume pairs

When the initial TCE copy is completed, the production and backup volumes
are said to be "Paired". The two paired volumes are referred to as the
primary volume (P-VOL) and secondary volume (S-VOL). Each TCE pair
consists of one P-VOL and one S-VOL. When the pair relationship is
established, data flows from the P-VOL to the S-VOL.
While in the Paired status, new data is written to the P-VOL and then
periodically transferred to the S-VOL, according to the user-defined update
cycle.
When a pair is "split", the data flow between the volumes stops. At this time,
all the differential data that has accumulated in the local array since the last
update is copied to the S-VOL. This insures that its data is the same as the
P-VOL's and is consistent and usable data.
During normal TCE operations, the P-VOL remains available for read/write
from the host. When the pair is split, the S-VOL also is available for read/
write operations from a host.
Hitachi AMS 2000 Family TrueCopy Extended Distance User Guide
shows a typical TCE environment.
Figure 1-1: Typical TCE Environment
Overview
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