Hitachi TAGMASTORE MK-90RD011-25, User Manual

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38 Chapter 2 Overview of CCI Operations
2.6.1 Creating SnapShot
The CCI command for creating a COW SnapShot pair is the same as for ShadowImage. The
RAID storage system determines whether the pair is a ShadowImage or SnapShot pair by the
LDEV attribute of the S-VOL. A SnapShot pair is generated in the following two cases.
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When V-VOL unmapped to the S-VOL of SnapShot called OPEN-0V is specified as S-VOL.
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When S-VOL is not specified.
The V-VOL has the following characteristic.
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It is displayed as “OPEN-0V” to identify V-VOL easily via SCSI Inquiry or CCI.
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V-VOL unmapped to the S-VOL of SnapShot will reply to SCSI Inquiry, but Reading and/or
Writing will not be allowed. LDEV will reply the capacity setting as an LU to SCSI Read
Capacity.
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V-VOL became the S-VOL of SnapShot will reply to SCSI Inquiry, and Reading and/or
Writing will be allowed.
2.6.2 SnapShot Volume Specifications
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Allowable type of paired volume: The supported volume type is OPEN-V only for P-VOL,
and OPEN-0V for S-VOL.
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Number of volumes (SnapShot) can be paired: This depends on P-VOL capacity, SnapShot
pool capacity, and shared memory capacity on the RAID storage system.
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Duplicated writing mode: Copying on write.
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Number of mirror volumes: Up to 64 secondary volumes can be defined for each P-VOL.
2.6.3 SnapShot Volume Characteristics
Each paired volume consists of a primary volume (P-VOL) and a secondary volume (S-VOL).
Each volume has the status for controlling the state concerning the pairing.
The P-VOL controls the pairing state which is reflected on the status of the S-VOL. The
major pairing statuses are “SMPL”, “PAIR”, “PSUS”, “COPY”, and “RCPY”. The status is
changed when the CCI command is issued. A read or write request from the host is allowed
or rejected according to the status.