PowerMax and VMAX All Flash Solutions Design (Symmetrix Remote Data Replication/Synchronous (SRDF/S)) Flashcards
What is the relationship between SRDF/S and response time?
w/ SRDF/S host response times will significantly increase resulting in application timeouts
What is key to make sure response time isn’t an issue when using SRDF/S?
ensure there are links to keep utilization around 50% to minimize response time
What causes the increase in response time when using SRDF/S?
data must be transmitted to remote site before write can be acknowledged
Symmetrix microcode and type of remote adapter
What is the effect of write block size on SRDF/S design?
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)
How should you size bandwidth for SRDF/S?
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
What unwanted data should be filtered for bandwidth sizing?
paging space
test file systems
file systems used for database reorgs
temporary files
What observations should be accounted for once unwanted data is taken out for bandwidth sizing?
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
What determines the amount of round trips w/ each IO for SRDF/S?
depends on the remote adapter and network extension equipment in use
What is the relationship between response time and distance?
response time will be affected by the distance and the number of round trips
What is the speed of light?
186.2m per ms (300km)
How much time does a round trip take?
2ms
When is an IO considered completed with synchronous replication?
not until it has made a round trip
What is the minimum number of round trips necessary for SRDF/S?
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
What is the network overhead consideration for SRDF/S using FC?
w/ SRDF/FC or DWDM implementations the Protocol converter delay for switches is considered insignificant
What is the network overhead consideration for SRDF/S using GbE?
IP networks require qualification to ensure that have sufficient quality to carry replication workloads without significant packet loss and inconsistent packet arrival
How do you determine the appropriate number of remote adapters for SRDF/S?
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
What is best practice for # of remote adapter design?
design for 50% utilization to allow for fluctuation and growth
What effect does SRDF/S have on the number of writes/sec that a volume can sustain?
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
How do you calculate the new response time of volumes due to SRDF/S implementation?
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
How do you calculate the maximum number of writes per second?
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
How should a customer resolve existing volume write limit issues?
either try to increase the volume write limits or try to reduce the writes/sec per volume that the application is performing
How should you tailor SRDF/S design?
should be tailored to satisfy the writes to the busiest volumes
most writes are concentrated on a few volumes
