EMC VMAX 100K - SRDF;A MSC Cycle Switching - Multi-Cycle Mode

Figure 33 SRDF/A MSC cycle switching – multi-cycle mode
Primary Site
Secondary Site
Capture
cycle
Apply
cycle
N-M Transmit
cycle
Receive
cycle
{
SRDF
consistency
group
Apply
N-M-1
Capture
N
Transmit
N-M
R2
R1
Receive
N-M
Transmit queue
depth = M
Transmit
N-1
R1
R1
R1
R2
R2
R2
R2
SRDF cycle switches all SRDF/A sessions in the MSC group at the same time. All
sessions in the MSC group have the same:
l
Number of cycles outstanding on the R1 side
l
Transmit queue depth (M)
In SRDF/A MSC sessions, Enginuity or HYPERMAX OS performs a coordinated cycle
switch during a window of time when no host writes are being completed.
MSC temporarily suspends writes across all SRDF/A sessions to establish
consistency.
Like SRDF/A cycle switching, the number of cycles on the R1 side varies depending on
whether one or both the arrays in the solution are running HYPERMAX OS.
SRDF/A MSC sessions that include an array running Enginuity 5773 to 5876 have only
two cycles on the R1 side (legacy mode).
In legacy mode, the following conditions must be met before an MSC cycle switch can
take place:
l
The primary array’s transmit delta set must be empty.
l
The secondary array’s apply delta set must have completed. The N-2 data must be
marked write pending for the R2 devices.
Write operations in cascaded SRDF
In cascaded configurations, R21 devices appear as:
l
R2 devices to hosts connected to R1 array
l
R1 device to hosts connected to the R2 array
I/O to R21 devices includes:
l
Synchronous I/O between the production site (R1)and the closest (R21) remote
site.
l
Asynchronous or adaptive copy I/O between the synchronous remote site (R21)
and the tertiary (R2) site.
l
You can Write Enable the R21 to a host so that the R21 behaves like an R2 device.
This allows the R21 -> R2 connection to operate as R1 -> R2, while the R1 -> R21
connection is automatically suspended. The R21 begins tracking changes against
the R1.
The following image shows the synchronous I/O flow in a cascaded SRDF topology.
Remote replication solutions
SRDF write operations 131