Thanks to this group, I successfully implemented DrivePool as a "RAID 1" software solution to mirror drives in case of one fails. I have 2x2TB in a pool mirrored in my PC. This way, kind of secured my live works from one possible failure.
I'm a photographer and I keep my shoots in external HDDs. Mostly WD My Passports, I'm not so proud of this, I learnt in the past days that they doesn't have standard SATA connectors...). I always tried to copy shoots at least to two drives, but you know how it goes, manually doing something not represents 100% coverage. I thought about DAS or even simpler external 2-bay HDD enclosures (I don't need RAID0, RAID1 and JBOD switches) and mirroring them with DrivePool. BUT the problem remains: at the certain point of time a photoshoot only will be represented powered on my PC: once on a 2X2TB pool and another mirrored pool connected to my PC via USB or eSATA. Single point of falure still presents, doesn't matter everything is on four drives and in two pools.
Is there any software, which does what's in the title, able to compare a drive (or folders) presented in my PC with a previous offline drive, that is already cached? So I want to still copy my data to external drives one at a time, I just don't want to hook up to my PC everything at once.