Hitachi AMS2100 User Manual page 45

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Table 1-8
ShadowImage is possible when a P-VOL of SnapShot and an S-VOL of
ShadowImage are the same LU.
Paired
(Includi
SnapShot P_VOL
Paired
Internal
Synchro
nizing)
Paired
R
x
Reverse
Synchronizing
Split
R
Failure
R
x
Failure (Restore)
Hitachi AMS 2000 Family Copy-on-Write SnapShot User Guide
Performance at the time of cascading the P-VOL of
SnapShot and the S-VOL of ShadowImage.
configuration in which the P-VOL of SnapShot and the S-VOL of
ShadowImage are cascaded, when SnapShot pair status is Split,
and the ShadowImage pair status is any of Paired, Paired
Internally Synchronizing, Synchronizing, and Split Pending,
the host I/O performance for the P-VOL of ShadowImage
deteriorates. Use ShadowImage in the Split status and, if needed,
resynchronize the ShadowImage pair and acquire the backup.
shows whether a read/write from/to an S-VOL of
Table 1-8: A Read/Write Instruction to a S-VOL of
Reve
ng
rse
Synchroni Sync
zing hroni
y
zing
R R
x x
R R
R R
x x
indicates a possible case, x indicates an impossible case
∆
indicates a case where a pair operation causes an error (a case that
can occur as a result of a change of the pair status to Failure)
R/W: Read/Write by a host is possible.
R: Read by a host is possible but write is impossible.
W: Write by a host is possible but read is impossible.
R/W: Read/Write by a host is impossible.
SnapShot overview
ShadowImage
ShadowImage S-VOL
Split
Split Pendin Failure
g
R/W R/W R
x x
R/W
R/W R/W R
R/W R/W R
∆ ∆
x
R/W R/W
In the
Failure Failure
(Restor (S_VOL
e) Switch)
R/W R/W
x x
∆
?
R/W R/W
∆
R/W R/W
x x
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