Why would an SSD boot even when not powered ?

Sebastian42

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Apr 6, 2015
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The question is only to meet the demands of the format of this forum. I was hoping someone could just make sense of the strange phenomenon I will describe below.
I use multiple HDDs on three PCs. I need to change between HDDs a lot, and I would rather avoid removing and replacing leads, so I bought 4-switch units with the form-factor of a strip such as is normally on the end of a PCI card. There is a LED indicator associated with each switch. After some weeks, the 4 switches lost their independence and so the unit became less useful. So I bought a number of others but the experience was repeated with each 'set of 4 switches'. I have also bought one at twice the price of the originals - its form-factor resembles a floppy disc drive. So far it has behaved as required/desired, but it is early days.
I will describe the difference experienced in the three PCs.
PC1 - Four spinning-disk HDDs - the 'strip' switch works fine.
PC2 - Three SSDs and one spinning-disk HDD - the more expensive switch is OK.
PC3 - Three spinning-disk HDDs and one SSD
PC2 & PC3 - The strip-switch LEDs light up 'randomly'.
PC2 - The floppy-disc-form-factor switch has not yet failed, but only one week has passed.
PC3 - Having figured that the mixture of SSDs and spining-disk HDDs on the same strip-switch spells trouble, I connected the strip-switch to only spinning-disk HDDs and so far it has behaved well. To be able to isolate the SSD, I fitted a molex-power switch between the SSD and the PSU, with (obviously) a molex-to-SATA power adapter to the SSD. The SSD ignored the On/Off setting of the molex-power-switch, and so the PC booted from the SSD irrespective of the molex-power-switch setting. I have tested the switch unit of the molex-power-switch with a digital multimeter which showed low resistance when closed and high resistance when open, so the switch WORKS.

1. It seems that an SSD remains powered, when a spinning-disk HDD would be off.
2. Switching both SSDs and spinning-disk HDDs causes problems EVENTUALLY.
Any enlightenment would be welcome.
 

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