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The relationship between an SRDF emulation and the resources on a director is
fixed: 1 director/1 CPU core/1 port. If more connectivity or IOPS are needed,
another SRDF emulation is required.
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Arrays can establish SRDF relationship with up to 32 other arrays.
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If a port gets “hot” performance may suffer, even if there are unused CPU
resources on the board.
Mixed configurations: HYPERMAX OS and Enginuity 5876
For configurations where one array is running Enginuity 5876, and the second array is
running HYPERMAX OS, the following rules apply:
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On the 5876 side, an SRDF group can have the full complement of directors, but
no more than 16 ports on the HYPERMAX OS side.
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You can connect to 16 directors using one port each, 2 directors using 8 ports
each or any other combination that does not exceed 16 per SRDF group.
SRDF consistency
Many applications (in particular, DBMS), use dependent write logic to ensure data
integrity in the event of a failure. A dependent write is a write that is not issued by the
application unless some prior I/O has completed. If the writes are out of order, and an
event such as a failure, or a creation of a point in time copy happens at that exact
time, unrecoverable data loss may occur.
An SRDF consistency group (SRDF/CG) is comprised of SRDF devices with
consistency enabled.
SRDF consistency groups preserve the dependent-write consistency of devices within
a group by monitoring data propagation from source devices to their corresponding
target devices. If consistency is enabled, and SRDF detects any write I/O to a R1
device that cannot communicate with its R2 device, SRDF suspends the remote
mirroring for all devices in the consistency group before completing the intercepted
I/O and returning control to the application.
In this way, SRDF/CG prevents a dependent-write I/O from reaching the secondary
site if the previous I/O only gets as far as the primary site.
SRDF consistency allows you to quickly recover from certain types of failure or
physical disasters by retaining a consistent, DBMS-restartable copy of your database.
SRDF consistency group protection is available for both SRDF/S and SRDF/A.
SRDF data compression
Compression minimizes the amount of data transmitted over an SRDF link.
Both software and hardware compression can be activated simultaneously for SRDF
traffic over GigE and Fibre Channel. Data is first compressed by software and then
further compressed by hardware.
Hardware compression is available through a compression I/O module. Each engine
supports a pair of compression I/O modules.
You can control hardware and software compression using EMC host-based SRDF
software or Unisphere for VMAX.
Software and hardware compression can be enabled on both the R1 and R2 sides, but
the actual compression happens from the side initiating the I/O (typically the R1 side).
Remote replication solutions
126 Product Guide VMAX 100K, VMAX 200K, VMAX 400K with HYPERMAX OS
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