On the space efficiency issue
After someone corrected the mistake in the original article (why didn't Pure Storage bother to make him correct it in the original text?), it turns out that Pure translates 366TB raw flash to 1PB effective capacity. Assuming the data reduction they use for that calculation is 5:1, the physical capacity they produce from the 366TB raw flash is 200TB, which means space efficiency of 55%. Indeed not the best (though not the worst either).
One thing should be noted, they use raw NAND flash for that calculation. Flash array vendors that use SSDs (as opposed to flash modules) use the SSD capacity as their "raw capacity", ignoring the over provisioning of nand flash inside the SSD. But someone has to pay for that extra flash storage!
If all AFA vendors would include the SSD over-provisioning in their space efficiency calculation, Pure's would look better. FWIW, the claim they make that DirectFlash saves flash over-provisionoing is technically sound.
The bottom line that counts is the price (or TCO) per TB, and the effective/raw ratio is only part of that deal.