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Hitachi Command Control Interface (CCI) User and Reference Guide 37
2.6 Overview of Copy-on-Write Snapshot Operations
Copy-on-Write Snapshot normally creates virtual volumes for copying on write without
specifying LUNs as S-VOLs. However, to use a SnapShot volume via the host, it is necessary
to map the SnapShot S-VOL to a LUN. Therefore, CCI provides a combined command to
enable the user or APP to use the same CCI command in order to maintain the compatibility
of ShadowImage.
SnapShot uses two techniques called V-VOL mapping and SnapShot using copy on write. Also
SnapShot volumes are put into pooling volumes called SnapShot pool, and the SnapShot pool
are specified as pool ID when a SnapShot is made. The SnapShot and volume mapping is
illustrated in Figure 2.19.
SnapShot pool
PVOL
10
0
VVOL
10-1
1
STD Inquiry
OPEN-0V
LDEV 20
SVOL
10-0
LDEV
20
2
VVOL
10-2
VG1
VG1
VG0
VG2
CL1-B CL1-C
LDEV
22
STD Inquiry
OPEN-0V
LDEV 22
Figure 2.19 Copy-on-Write Snapshot and Volume Mapping