Systems Research Laboratory

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Additional Comments:
  * The authors do not evaluate with real random I/Os. 
  * Deletion of blocks or cleaning fragmented blocks to reclaim space and reduce fragmentation is never addressed. 
  * This approach is very similar to MFT. It would be nice to see a comparision.
  * Instead of ext2, this work should be compared to a log file system because of the similarities.


Main reviewer additional comments:
  * Flexible I/O benchmark seems to be oriented to testing random IO patterns. However, it is not clear on the paper how this random IO patterns are executed, or what the tool does indeed. The reference site "[5] http://freshmeat.net/projects/fio/" does not provide further explanation in this respect, either. So still improvements in random write patterns is yet to be shown explicitly since Figure 8 shows different response type improvements depending on the device, e.g. Mtron experiment shows reduction in response time of a modest 25%. Thus, the proposed technique does not uniformly benefit all devices.
  * A better explanation of the improvements seen is that by allocating SSD free blocks from different segments, you are using distinct allocation pools in the device, thus avoiding expensive full merge operation because you'll be distributing random write logs on more free log blocks.
  * Missing Managed-Flash Technology performance comparison when measuring random write improvements.