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Issue: How to configure long distance mode between Production Site and Dr Site with the distance of 34KM?
Solution description: Provided portCfgLongDistance command guide
Requirements: License for FC port to allow long distance configuration above 10KM
Rough network topology based on client information: Two SNS2248 device on each site (Total of 4) (Production and Dr), both side connected through port 23 over distance of 34KM. Cascadely connected. Therefore 4 ports need to be configured, 1 of each SAN Switch FC port of the SNS2248.
1. During configuration, customer received a warning message “port (23) may be reserving more credits depending on port speed”.
Client used to set distance at 40, but leaving other value at default. Therefore, when client wants to set the distance to 34KM which is reduced from previous value, the buffer remains unchanged which may lead to showing the warning message stating that the port is reserving more credits.
Event log noticeable issue
2017/08/29-07:33:54, [FABR-1001], 210, FID 128, WARNING, ICBCI-HK1-MC1-SN2488-01, port 23, Incompatible Long distance mode.
!!Buffer credits are usually set automatically according to the distance provided unless any changes is made in between, therefore warning message such as reserving more/less credits!!
Client is advised to set the port configuration default, then start configuring the long distance mode according to their requirement.
ICBCI-HK1-SN2248-02:FID128: admin> portcfgdefault 23
ICBCI-HK1-SN2248-02:FID128: admin> portcfglongdistance 23 LS 1 –distance 34
However, if client wants to manually adjust the buffer credits there is a formulae to it:
Either formula depends on whether QoS is enabled or disabled.
For client requirement distance: 34KM
QoS enabled buffer size = (34 * 2Gbps / 2) + 6 + 14 = 54
QoS disabled buffer size = (34 * 2Gbps / 2) + 6 = 40
Use one of the following formulas to calculate the reserved buffers for distance:
• If QoS is enabled:
(Reserved Buffer for Distance Y) = (X * LinkSpeed / 2) + 6 + 14
• If QoS is not enabled:
(Reserved Buffer for Distance Y) = (X * LinkSpeed / 2) + 6
The formulas use the following parameters:
X = The distance determined in step 1 (in km).
LinkSpeed = The speed of the link determined in step 2.
6 = The number of buffer credits reserved for fabric services, multicast, and broadcast
traffic. This number is static.
14 = The number of buffer credits reserved for QoS. This number is static.
Using 50 km as the desired distance of the switch-to-switch connection and 2 Gbps as the
speed of the long-distance connection, insert the numbers into the appropriate formula. The
formula should read as follows:
(50 km * 2 Gbps / 2) + 6 = 56 buffers, which is the number of buffers reserved for distance.
The following examples use different speeds, all based on a distance of 50 km. The distances and
speeds are variables that can change depending on how your network is set up.
• If you have a distance of 50 km at 1 Gbps, then (50 km * 1 Gbps / 2) + 6 = 31 buffers.
• If you have a distance of 50 km at 2 Gbps, then (50 km * 2 Gbps / 2) + 6 = 56 buffers.
• If you have a distance of 50 km at 4 Gbps, then (50 km * 4 Gbps / 2) + 6 = 106 buffers.
• If you have a distance of 50 km at 8 Gbps, then (50 km * 8 Gbps / 2) + 6 = 206 buffers.
• If you have a distance of 50 km at 10 Gbps, then (50 km * 10 Gbps / 2) +6 = 256 buffers.
• If you have a distance of 50 km at 16 Gbps, then (50 km * 16 Gbps / 2) + 6 = 406 buffers.
After all SAN switch is equally configured, there is no more warning message.
2017/08/31-16:38:05, [PORT-1010], 220, FID 128, INFO, ICBCI-HK1-MC1-SN2488-01, Port (ID: 23) QoS is disabled.
2017/08/31-16:40:20, [LOG-1000], 221, FID 128, INFO, ICBCI-HK1-MC1-SN2488-01, Previous message repeated 1 time(s).
2017/08/31-16:40:20, [SEC-1203], 222, FID 128, INFO, ICBCI-HK1-MC1-SN2488-01, Login information: Login successful via TELNET/SSH/RSH. IP Addr: 10.128.12.16