Linked by Thom Holwerda on Thu 27th Sep 2012 19:36 UTC
Apple I bought a brand new iMac on Tuesday. I'm pretty sure this will come as a surprise to some, so I figured I might as well offer some background information about this choice - maybe it'll help other people who are also pondering what to buy as their next computer.
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RE: Something important missing
by Alfman on Thu 27th Sep 2012 21:10 UTC in reply to "Something important missing"
Alfman
Member since:
2011-01-28

bowkota,

Even though SSD's are becoming affordable, I'm not keen on their falling reliability levels. First there was SLC - 1 bit per cell, then MLC with 2 bits per cell (4 voltage levels). Now we're seeing 3 bits per cell (8 distinguishable voltage levels). This produces higher capacity drives for very low manufacturing costs.

Each generation is moving towards ever smaller manufacturing processes: from 100nm in 2007 to 20nm today. This means more cells per area, but also that fewer electrons are available to represent a bit state, and increasing the likelihood of getting stuck electrons.

Combine both of these trends and it spells disaster for reliability. I experienced my own data loss, which is why I've been researching these things.

I looked up the specs for NAND chips used in my device, and they officially only spec 3K program/erase cycles before loosing data integrity!!! This is much lower than the million write cycles we had using 100nm SLC NAND.

3,000 P/E cycles (with 24 bit/ 1,024byte ECC)

http://www.jm-chip.com/en/down/H27UBG8T2A.pdf
(link is down)

http://forums.anandtech.com/showthread.php?t=2144579
(they talk about it here)

Flash devices use smart controllers to distribute the writes across all cells of the NAND chip to alleviate the effects of any individual sector updates on the logical media. This is fine assuming most sectors rarely change. However if you have a data load that routinely rewrites significant portions of the flash disk - then the average cell lifespan will be consumed fairly quickly. Due to the write-distribution algorithm there is a good chance that all NAND pages will reach EOL at approximately the same time, so once data errors are discovered, there are probably more errors that haven't even been discovered yet.

Not saying it's for nobody, but do your research... failure is common. By all means keep backups! ( Ideally not on flash drives ;) )

I've been trying my own hand at performing data recovery off failing flash media, so if anyone does get unrecoverable flash media, I might be able to offer my services ;)

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