Amazon hasn't publicly stated what technology Glacier is based on.
It's been speculated that instead of throwing out previous generation AWS hardware, they're simply repurposing then into cheap storage nodes for Glacier.
I can well imagine it started that way, but the density of tape over disk makes it seem likely to me that by now they're on custom versions of Spectra tape libraries, which pretty much fits into the "Try selling it, if it sells, make something cheap to run it" philosophy.
It's been speculated that instead of throwing out previous generation AWS hardware, they're simply repurposing then into cheap storage nodes for Glacier.