PowerMax and VMAX All Flash Solutions Design (Symmetrix Remote Data Replication/Synchronous (SRDF/S))

Question 1

What is the relationship between SRDF/S and response time?

Answer 1

w/ SRDF/S host response times will significantly increase resulting in application timeouts

Question 2

What is key to make sure response time isn’t an issue when using SRDF/S?

Answer 2

ensure there are links to keep utilization around 50% to minimize response time

Question 3

What causes the increase in response time when using SRDF/S?

Answer 3

data must be transmitted to remote site before write can be acknowledged

Symmetrix microcode and type of remote adapter

Question 4

What is the effect of write block size on SRDF/S design?

Answer 4

larger block size applications will suffer higher response time impact as compared to smaller block size applications

data transfer time is directly proportional to block size (EX: 4K block size can be transferrd in .4s (4/10)

Question 5

How should you size bandwidth for SRDF/S?

Answer 5

filter out unwanted datasets or files - if data is not required for remote restart it should not be mirrored

ensure that max bandwidth is provided by the network at all times

Question 6

What unwanted data should be filtered for bandwidth sizing?

Answer 6

paging space
test file systems
file systems used for database reorgs
temporary files

Question 7

What observations should be accounted for once unwanted data is taken out for bandwidth sizing?

Answer 7

allow for growth
add allowance for peaks
divide total MB/# of seconds in interval to get MB/s
to calculate compressed bandwidth requirement further divide by compression ratio

Question 8

What determines the amount of round trips w/ each IO for SRDF/S?

Answer 8

depends on the remote adapter and network extension equipment in use

Question 9

What is the relationship between response time and distance?

Answer 9

response time will be affected by the distance and the number of round trips

Question 10

What is the speed of light?

Answer 10

186.2m per ms (300km)

Question 11

How much time does a round trip take?

Answer 11

2ms

Question 12

When is an IO considered completed with synchronous replication?

Answer 12

not until it has made a round trip

Question 13

What is the minimum number of round trips necessary for SRDF/S?

Answer 13

2 round trips for FC

latency can be reduced to 1round trip if write acceleration/FAST Write/SiRT equipment is used for FC

1 round trip for GbE

Question 14

What is the network overhead consideration for SRDF/S using FC?

Answer 14

w/ SRDF/FC or DWDM implementations the Protocol converter delay for switches is considered insignificant

Question 15

What is the network overhead consideration for SRDF/S using GbE?

Answer 15

IP networks require qualification to ensure that have sufficient quality to carry replication workloads without significant packet loss and inconsistent packet arrival

Question 16

How do you determine the appropriate number of remote adapters for SRDF/S?

Answer 16

depends on the write workload (write/s and block size) and type of remote adapters w/ specific microcode level

number of writes per second / the maximum number of IOPS

Question 17

What is best practice for # of remote adapter design?

Answer 17

design for 50% utilization to allow for fluctuation and growth

Question 18

What effect does SRDF/S have on the number of writes/sec that a volume can sustain?

Answer 18

in an SRDF/S solution the extended response time can lower the writes/sec a volume can sustain

analysis needs to be performed to identify all the volumes that will hit the write limits

Question 19

How do you calculate the new response time of volumes due to SRDF/S implementation?

Answer 19

if no performance data available use standardized response time (SRT)

SRT = response time w/o SRDF/S + data transfer time + propagation delay + network equipment delay

Question 20

How do you calculate the maximum number of writes per second?

Answer 20

volume write limits (VWL) = 1/SRT

VWL should be greater than the numbers of writes/sec that an application is currently performing without SRDF/S

Question 21

How should a customer resolve existing volume write limit issues?

Answer 21

either try to increase the volume write limits or try to reduce the writes/sec per volume that the application is performing

Question 22

How should you tailor SRDF/S design?

Answer 22

should be tailored to satisfy the writes to the busiest volumes

most writes are concentrated on a few volumes