Scrambling Data to Improve Reliability?

I secure erase all SSDs before I run any test, unless I'm testing used performance. On a modern SSD, performing an ATA Secure Erase takes anywhere from 30 - 50 seconds in most cases. The first time I went to secure erase the SiliconEdge Blue it took almost 17 minutes. I asked Western Digital what was going on, and got an interesting explanation.

The smaller NAND flash gets, the more prone the cells are to developing bit errors. That's why SandForce made such a big deal out of its controllers making 34nm possible thanks to extra error correction and redundancy.

SandForce's controllers attempt to fix bit errors in order to enable the use of cheaper MLC NAND

Western Digital found that writing certain combinations of data were more prone to generating these bit errors on smaller dimension flash (< 50nm). To prevent these sorts of errors from cropping up, the controller reorganizes (or scrambles) the data it's fed before writing it to the flash. When you go back to read the data off the flash, it's unscrambled before sending it back to the host controller so you get the data you requested.

As a side effect, the controller can't simply perform a flash erase to zero out the contents of the drive. Instead the SiliconEdge Blue has to physically write (a F or 0) to every NAND flash cell on the drive itself, which takes some time. On the bright side, WD does this to improve data integrity (or more likely to use cheaper MLC NAND without sacrificing reliability). The only downside is that a secure erase, which you shouldn't need to do that often, will take a long time to complete.

The Controller Sequential Read/Write Speed
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  • The0ne - Monday, March 8, 2010 - link

    Sorry, but it's price. The technology WILL improve this year. Just based on what you've said, you're talking about the drives being 50% faster than 1960s tech. That's really not saying much as we all know the HD is the bottleneck.

    I really would like to have a speedy SSD but I'm not going to spend that much on so little (space), even if I could afford them. Just wait a bit more this year and we'll see competition driving prices down :)
  • coolkev99 - Thursday, March 4, 2010 - link

    But yeah.. the price is waaay to high.
  • leexgx - Thursday, March 4, 2010 - link

    on this site they managed to make the SSD do the dreaded 0.02MB/s Write issues that the 602 or 602b had under Random Write loads it was doing 2 IOPS as well">
  • leexgx - Thursday, March 4, 2010 - link

    this shows bit more of the issue not been able to keep up under constant Write load doing 0.02MB/s">

    my last link was relating to IOPS

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