IBM System storage DS6000 Series, Redbook

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Chapter 23. Global Mirror options and configuration
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23.6.2 Single site host connectivity
Figure 23-8 Single site host connectivity - with or without FICON connectivity between sites
Figure 23-8 shows a single host configuration example. This is again a 2-site disaster
recovery solution, although there are no hosts on one of the sites, the recovery site. Recovery
is provided at the storage disk subsystem level—data recovery.
Depending on how far apart the two sites are from each other, there are two basic
approaches to managing this configuration:
1. The sites are at FICON distance.
This allows you to connect the host to both sites and manage either site from the host via
conventional Global Mirror inband commands. Such a configuration may use cascaded
FICON directors to interconnect both sites using FICON channels. In case of a primary
site failure, limited to storage disk subsystems, the failover may be managed from the local
host. See 23.7, “Recovery scenario after primary site failure” on page 282.
2. The two sites are not interconnected over FICON due to extended distances, or the
required network technology for FICON is not available.
Global Mirror management of the remote storage disk subsystems can be done through
inband commands from the local site. This is limited to FlashCopy operations only.
Besides the TSO and ICKDSF inband FlashCopy commands, you may consider using DS
CLI commands.
Recovery operations as described in 23.7, “Recovery scenario after primary site failure”
on page 282 require host connectivity at the remote site when utilizing TSO or ICKDSF-
based Global Mirror commands. To quickly recover the remote site you may consider
using DS CLI commands, which do not require any host connectivity.
Note: This scenario is ideal for a synchronous solution, such as Metro Mirror. Metro
Mirror provides zero data loss with almost no impact to host I/O at short distances.
Additionally, Metro Mirror environments tend to be less complex than Global Mirror
environments.
Remote site Local site
Primary
Primary
A
B
Secondary
Primary
Primary
C
Tertiary
PENDING
Primary
Primary
A
B
Secondary
Primary
Primary
C
Tertiary
PENDING
Primary
Primary
A
B
Secondary
Primary
Primary
C
Tertiary
PENDING
Primary
Primary
A
A
Primary
PENDING
01
Primary
Primary
A
A
Primary
PENDING
01
Primary
Primary
A
A
Primary
PENDING
01
Host
FICON FICON FCP FCP
FICON/FCP director(s) FICON/FCP director(s)
Host
channels
Global Mirror
session links
FICON Channels
Global Copy
links
ISLs
Global Mirror
session links
Host
channels