I would grab a WD drive.... not a fanboy or anything just my experience with seagate in the past few years has been terrible.
get a WD blue or black (black is dual processor)
I have had two of those models you speak of die on me in the last year, I bought a asus laptop and it came with two of them, had to swap them out... bad sectors on both
I havent seen those drives forsale in a long time, my understanding was they stopped making them... basically flash memory only has so many writes, so using it in that way leads to failure pretty quick
compared to just having a SSD and a HDD (writing as much as you can to your HDD)
I strongly recommend avoiding that brand name alltogether (just in my personal experience)
as far as backing it up goes, anything 120gb or bigger will work.... if you have that 120gb laying around that will work fine, but it is not something I would go out and buy just because I havent seen 120gb drives around in years, smallest you can buy in a store these days is a 320.
PS3 SLIM - 3.50 OFW> 3.55 OFW> 3.55 GEOHOT CFW> 3.55 WUTANGRZA CFW> 3.55 KMEAW CFW> 3.55 REBUG CFW> 3.55 JB2USB TB CFW> 3.55 REBUG TB CFW> 4.21 ROGERO v1.00> 4.30 ROGERO v1.03> 4.30 ROGERO 2.00> 4.30 ROGERO 2.03> 4.30 REBUG