SG0-001 · Question #594
A switch with 8Gb ports has been connected with five hosts running at 4Gb speed and two at 2Gb speed. If the switch is communicating through an ISL with another 8Gb switch where the storage array is c
The correct answer is C. 3:1. This question requires calculating the oversubscription ratio of a switch's uplink (ISL) by comparing the aggregate bandwidth of connected hosts to the ISL's bandwidth.
Question
A switch with 8Gb ports has been connected with five hosts running at 4Gb speed and two at 2Gb speed. If the switch is communicating through an ISL with another 8Gb switch where the storage array is connected, which of the following will be the oversubscription ratio of this configuration?
Options
- A1:1
- B2:1
- C3:1
- D5:1
How the community answered
(32 responses)- A3% (1)
- B13% (4)
- C78% (25)
- D6% (2)
Why each option
This question requires calculating the oversubscription ratio of a switch's uplink (ISL) by comparing the aggregate bandwidth of connected hosts to the ISL's bandwidth.
The total ingress bandwidth from the connected hosts is calculated as (5 hosts * 4Gb/s) + (2 hosts * 2Gb/s) = 20Gb/s + 4Gb/s = 24Gb/s. Since the ISL uplink to the storage array is 8Gb/s, the oversubscription ratio is the total host bandwidth divided by the uplink bandwidth, which is 24Gb/s / 8Gb/s = 3:1.
A 5:1 ratio would imply the total host bandwidth is five times the uplink bandwidth, requiring 40Gb of host traffic for an 8Gb uplink, which is much higher than the calculated 24Gb.
Concept tested: Fibre Channel oversubscription ratio calculation
Source: https://www.cisco.com/c/en/us/products/collateral/storage-networking/mds-9000-series-multilayer-switches/prod_white_paper0900aecd8058223d.html
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