Why there are 2 SSDs on each cache board, in VSP.
The CM PCB should contain atleast one SSD. The second SSD is required depending on how much cache memory capacity is installed. When performing a cache upgrade, the SVP application will indicate that a second SSD is needed.
Also the SSD's operate independently, and there is no RAID between the two SSD's. The second SSD provides additional storage capacity when the amount of cache on the PCB is large.
The reason for two SSD drives is that current available SSD capacities are 32 GB and 64 GB decimal. But in actual its 31.5 GB binary and 63 GB binary. So for example if you have only 32 GB cache on one board then one 32 GB ( 31.5 GB Actual ) SSD won't be enough to hold that data and that's why you will need two SSD drives. Below is screenshot from concepts guide for VSP
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