PowerMax and VMAX All Flash Solutions Design (SRDF/A Design Architecture and Resiliency Features)

Question 1

What happens to SRDF/A if the local or remote array are running Enginuity 5876?

Answer 1

SRDF/A operates in legacy mode

Question 2

How does SRDF/A work?

Answer 2

uses delta sets to maintain a group of writes over a short period of time

Question 3

What are delta sets?

Answer 3

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

Question 4

What are the 4 types of delta sets that legacy SRDF/A must manage?

Answer 4

capture delta set
transmit delta set
receive delta set
apply delta set

Question 5

What is the capture delta set?

Answer 5

captures in cache all incoming writes to the source volumes in the SRDF/A group

Question 6

What is the receive delta set?

Answer 6

in the target system - in the process of receiving data from Transmit Delta Set

Question 7

What is the transmit delta set?

Answer 7

contains data from the immediately preceding delta set - this data is being transferred to the remote system

Question 8

What is the apply delta set?

Answer 8

older data set contained in the target - data from apply delta set is being assigned to appropriate cache slots ready for destaging to disk

Question 9

How do deltas change in a cycle switch?

Answer 9

new delta set = N+1 - becomes capture set
transmit/receive set = N
apply delta set = N-1

Question 10

What is write folding?

Answer 10

repeat writes into a cycle are sent once

leads to reduction in link bandwidth usage

Question 11

What is SRDF/A Single-Session Consistency (SSC)?

Answer 11

sessions where both arrays are running PowerMaxOS or HYPERMAX OS have one or more transmit cycles on the R1 side (multi-cycle mode)

Question 12

What is SRDF/A Multi-Session Consistency (MSC)?

Answer 12

sessions where both arrays are running PowerMaxOS or HYPERMAX OS have two or more transmit cycles on the R1 side (multi-cycle mode)

Question 13

How does cycle switching work in legacy SRDF/A?

Answer 13

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

Question 14

How does cycle switching work in multi-cycle mode (MCM) SRDF/A?

Answer 14

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

Question 15

What effect does the cycle switching of legacy SRDF/A have on performance?

Answer 15

delays in cycle switching can lead to large delta sets and unpredictable RPO on the R2 side

Question 16

What effect does the cycle switching of MCM SRDF/A have on performance?

Answer 16

RPO at R2 side is more granular and predictable

Question 17

What is Transmit Idle in regards to SRDF/A?

Answer 17

keeps the SRDF/A session allowing for recovery that does not require user intervention during short term network interruptions

Question 18

How does Transmit Idle work?

Answer 18

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

Question 19

What is Delta Set Extension (DSE)?

Answer 19

if the system approaches the maximum SRDF/A cache utilization threshold DSE offloads some or all of the delta set data

Question 20

What is the recommendation for DSE configuration?

Answer 20

recommended that both sides use the same configuration of DSE on both sides

Question 21

How does DSE work?

Answer 21

works in tandem w/ group-level write pacing to prevent cache overutilization during spikes in IO or network slowdowns

Question 22

How does DSE work w/ HYPERMAX OS or PowerMaxOS?

Answer 22

offload data into a Storage Resource Pool

DSE can use a Storage Resource Pool pre-configured specifically for DSE

Question 23

How does DSE work w/ Enginuity 5876?

Answer 23

offloads data to a DSE pool that you configure

to use DSE each SRDF group must be explicitly associated w/ a DSE pool

Question 24

What happens in SRDF/A if R1 is running PowerMax/HYPERMAX OS and R2 is running Enginuity 5876?

Answer 24

SRDF/A runs in legacy mode

DSE is disabled by default on both arrays

Question 25

What does write pacing do?

Answer 25

reduces the likelihood that an active SRDF/A session drops due to cache exhaustion

Question 26

What is write pacing?

Answer 26

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

Question 27

When is write pacing used?

Answer 27

to maintain SRDF/A replication w/ reduced resources when replication is more important for the application than minimizing response time

Question 28

How can write pacing be applied?

Answer 28

to groups or devices for individual SRDF/A pairs that have TimeFinder/Snap or TimeFinder/Clone sessions off the R2 devices

Question 29

What is group pacing?

Answer 29

adjusts the pace of host writes to match link transfer rate of the SRDF/A session

Question 30

What does group pacing depend on?

Answer 30

whether the maximum pacing delay is specified

Question 31

What happens to group pacing if maximum pacing delay is unspecified?

Answer 31

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

Question 32

What happens to group pacing if maximum pacing delay is specified?

Answer 32

SRDF adds up to the user specified maximum write pacing delay to keep the SRDF/A session running

Question 33

When does group pacing get activated?

Answer 33

activities that result in slow R2 operations

Question 34

How is write pacing supported for systems running PowerMaxOS or HYPERMAX OS?

Answer 34

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

Question 35

How is write pacing supported for systems running Enginuity?

Answer 35

SRDF/A device pacing applies a write pacing delay for individual SRDF/A R1 devices whose R2 counterparts participate in TimeFinder copy sessions