Challenge: Make Tux3 work well with flash disks

Hi all,

Please see this well written analysis of performance loss as a 
new-generation Intel flash disk "ages":

   http://www.pcper.com/article.php?aid=669
   "Long-term performance analysis of Intel Mainstream SSDs"

Though I have not really analyzed the issues completely at this time, I 
have the feeling Intel made a slight mistake in the way they combine 
writes.  I think that what they do is this: they have a "current" flash 
block, which starts fully erased, then each write transfer is appended 
until it is full.  So writes are combined in write order, which is a 
lot like the deduplication plan the Pune Institute students are 
pursuing.  The bucket idea is likely to have advantages and drawbacks 
similar to Intel's SSD write strategy.

The problem in both cases is the effect of rewrites, which cause data to 
be relocated away from its original position, leaving holes at the 
original position.  This may not be as big a problem with deduplication 
if the target application is mainly archive, but it is a serious and 
visible problem with a flash device that intends to act like a disk 
drive.

What happens is, when Intel's disk fills and ages, the best candidate 
block for erasing will have a high percentage of valid data on it, 
which has to be copied to a new location.  The performance of the disk 
under a steady write load will thus drop to a fraction of the erase 
speed, because a portion of data recovered by erasing has to be used to 
store valid data relocated from candidate erase blocks.