PowerMax and VMAX All Flash Solutions Design (SRDF/A Design Architecture and Resiliency Features) Flashcards
What happens to SRDF/A if the local or remote array are running Enginuity 5876?
SRDF/A operates in legacy mode
How does SRDF/A work?
uses delta sets to maintain a group of writes over a short period of time
What are delta sets?
groups of write consistent data that reside in different sections of PowerMax/VMAX cache
starting at 1 each delta set is assigned a numerical value that is one more than the preceding
What are the 4 types of delta sets that legacy SRDF/A must manage?
capture delta set
transmit delta set
receive delta set
apply delta set
What is the capture delta set?
captures in cache all incoming writes to the source volumes in the SRDF/A group
What is the receive delta set?
in the target system - in the process of receiving data from Transmit Delta Set
What is the transmit delta set?
contains data from the immediately preceding delta set - this data is being transferred to the remote system
What is the apply delta set?
older data set contained in the target - data from apply delta set is being assigned to appropriate cache slots ready for destaging to disk
How do deltas change in a cycle switch?
new delta set = N+1 - becomes capture set
transmit/receive set = N
apply delta set = N-1
What is write folding?
repeat writes into a cycle are sent once
leads to reduction in link bandwidth usage
What is SRDF/A Single-Session Consistency (SSC)?
sessions where both arrays are running PowerMaxOS or HYPERMAX OS have one or more transmit cycles on the R1 side (multi-cycle mode)
What is SRDF/A Multi-Session Consistency (MSC)?
sessions where both arrays are running PowerMaxOS or HYPERMAX OS have two or more transmit cycles on the R1 side (multi-cycle mode)
How does cycle switching work in legacy SRDF/A?
cycle switch is coupled between R1 and R2 arrays
a new capture cycle cannot start until the transmit cycle completes its commit of data from R1 side to R2
How does cycle switching work in multi-cycle mode (MCM) SRDF/A?
when the preset minimum cycle time is reached the R1 data collected during the capture cycle is added to the transmit queue and a new R1 capture cycle is started
there is no wait for the commit on the R2 side before starting a new capture cycle
What effect does the cycle switching of legacy SRDF/A have on performance?
delays in cycle switching can lead to large delta sets and unpredictable RPO on the R2 side
What effect does the cycle switching of MCM SRDF/A have on performance?
RPO at R2 side is more granular and predictable
What is Transmit Idle in regards to SRDF/A?
keeps the SRDF/A session allowing for recovery that does not require user intervention during short term network interruptions
How does Transmit Idle work?
data transmission from the source to the target is halted
MCM - cycle switching continues on the R1 side - multiple transmit delta sets accumulate on the source side
legacy - cycle switching stops and the capture cycle continues to grow
What is Delta Set Extension (DSE)?
if the system approaches the maximum SRDF/A cache utilization threshold DSE offloads some or all of the delta set data
What is the recommendation for DSE configuration?
recommended that both sides use the same configuration of DSE on both sides
How does DSE work?
works in tandem w/ group-level write pacing to prevent cache overutilization during spikes in IO or network slowdowns
How does DSE work w/ HYPERMAX OS or PowerMaxOS?
offload data into a Storage Resource Pool
DSE can use a Storage Resource Pool pre-configured specifically for DSE
How does DSE work w/ Enginuity 5876?
offloads data to a DSE pool that you configure
to use DSE each SRDF group must be explicitly associated w/ a DSE pool
What happens in SRDF/A if R1 is running PowerMax/HYPERMAX OS and R2 is running Enginuity 5876?
SRDF/A runs in legacy mode
DSE is disabled by default on both arrays
What does write pacing do?
reduces the likelihood that an active SRDF/A session drops due to cache exhaustion
What is write pacing?
dynamically paces the host IO rate so it does not exceed the service rate of the SRDF/A session
prevents cache overflow on both the R1 and R2 sides
When is write pacing used?
to maintain SRDF/A replication w/ reduced resources when replication is more important for the application than minimizing response time
How can write pacing be applied?
to groups or devices for individual SRDF/A pairs that have TimeFinder/Snap or TimeFinder/Clone sessions off the R2 devices
What is group pacing?
adjusts the pace of host writes to match link transfer rate of the SRDF/A session
What does group pacing depend on?
whether the maximum pacing delay is specified
What happens to group pacing if maximum pacing delay is unspecified?
SRDF adds up to 50ms to the host write IO response time to match the speed of either the SRDF links or the apply operation on the R2 side
What happens to group pacing if maximum pacing delay is specified?
SRDF adds up to the user specified maximum write pacing delay to keep the SRDF/A session running
When does group pacing get activated?
activities that result in slow R2 operations
How is write pacing supported for systems running PowerMaxOS or HYPERMAX OS?
write pacing is not supported for asynchronous R2 devices in TimeFinder or TimeFinder SnapVX sessions when either array in the configuration is running PowerMaxOS or HYPERMAX OS
How is write pacing supported for systems running Enginuity?
SRDF/A device pacing applies a write pacing delay for individual SRDF/A R1 devices whose R2 counterparts participate in TimeFinder copy sessions
