I would say lifespan shouldn't be a concern, as it will last so long you will most likely have replaced it with something bigger and faster. The problem I have with my undelivered 840 120 is speed (ordered it a week ago and still not delivered ffs). It doesn't seem that the write speed of 130 is holding it back, as it beats the 830 in Windows booting and program startup, but it does have a problem with garbage collection and the firmware that was released is a little too young for anyone to be able to give a clear answer as to whether it solves the problems with the drive or not.
UK.hardware.info is down (http://uk.hardware.info
). They have an exhaustive review of all 840 models. I was going to post links to their review, showing that the 840 is faster than the 830 in nearly all benchmarks, bar writing and even then in some they are equal. I highly recommend keeping an eye on this website and reading their review, it's quite interesting.
When it comes to longevity they state the 840 120 will last between 4 and 10 years. The longest I've kept an HDD is 2-3 years, after which it got replaced due to it simply being too small.
Of course, if you write 20GiB a day, the estimated lifespan will be halved, although we are still looking at several years. Even with 30GiB of writes a day the 256GiB TLC drive should be sufficient in terms of endurance. Write amplification can also go over 10x if your workload is heavily random write centric, but that is more common in the enterprise side - client workloads are usually much lighter.
Furthermore, it should be kept in mind that all SMART values that predict lifespan are conservative; it's highly unlikely that your drive will drop dead once the WLC or MWI hits zero. There is a great example at XtremeSystems where a 256GB Samsung SSD 830 is currently at nearly 6,000TiB of writes. Its WLC hit zero at 828TiB of writes, which means its endurance is over seven times higher than what the SMART values predicted. That doesn't mean all drives are as durable but especially SSDs from NAND manufacturers (e.g. Intel, Crucial/Micron, Samsung etc.) seem to be more durable than what the SMART values and datasheets indicate, which isn't a surprise given that they can cherry-pick the highest quality NAND chips.
While this is an MLC drive I would say that if a TLC drive lasts 2x the length of time they state it will it will last longer than your patience.Edited by Liranan - 12/14/12 at 11:42pm