If you are looking for a relatively affordable, high-capacity external (portable) SSD, check out the PNY EliteX-PRO. Its 4TB configuration is now available with a big 35% discount.
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You can currently get the very small PNY EliteX-PRO 4TB portable SSD for just $324.99 at Amazon, and other PNY portable SSDs are also seeing big discounts as well, for a limited time.