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January 31st, 2014 03:00
SRDF Round Trip Time (latency)
Hi All,
Is there any symcli command to determine Round Trip Time (latency) between 2 Symmetrix VMAX Array.
Let me explain the situation.
We have 2 VMAX arrays situated 20 KMs apart. The Arrays are connected to each other through FCIP. However, from Array to Switch it is FC.
The bandwidth between 2 sites is 100 Mbps.
At present we have deployed SRDF/A. Hence, we would like to know latency between the 2 sites in order to prepare for SRDF/S.
Any help is appreciated.....
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PedalHarder
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465 Posts
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February 2nd, 2014 13:00
There is no CLI command that displays SRDF latency. There is a small baseline overhead for and SRDF write, along with the distance penalty. At 20KM you are looking at ballpark 0.7ms.
Have you used SRDF/S previously? Please be aware of the SRDF/S outstanding writes rule...
(up to) one outstanding write per device per path (up to 8 paths).
For example, a host is presented a 4-way striped meta device and is presented down 4 FA paths. This device may have a maximum of 4X4=16 outstanding SRDF/S writes. If concurrent write demands are higher than that, you will see elongated response time.
Anonymous User
67 Posts
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February 3rd, 2014 00:00
Hello chinmay,
If you have a UNIX management host, a crude way to measure the Link latency between the sites would be to use the UNIX "time" command on a symdev show to query the R2 device replicated using SRDF/S (There should be a Windows equivalent too.)
For example, if you've got device 111 on Symmetrix 123 replicating to device 112 on Symmetrix 456, this is what you could use, on the SYMCLI host that has the boxes discovered ..
# time symdev show 111 -sid 123
# time symdev show 112 -sid 456 -- look for the 'real' time - this is the total time it took for the process to complete the call.
thanks.