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Comment by jacobscott | Hacker News Reader

Previously a 1TB, 4K PIOPS volume was $525/mo. With a 35% discount on PIOPS this now runs $385/mo, but you can also get 1TB, 3K PIOPS General Purpose volume for $100/mo. Pretty nice price drop!

Generally, since 1 GB of GP SSD costs as much as 1 PIOP, in most cases you should just purchase a max(DESIRED_VOLSIZE, DESIRED_PIOPS/3)GB GP SSD volume rather than a PIOPS volume. I think.

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The 3,000 IOPS figure for General Purpose SSDs comes with two caveats - it is available only in bursts for up to 30 minutes and it comes out of a capped reserve which is slowly refilled over time based on the size of the drive. In other words, it is not Provisioned IOPS.

If you wanted it to be true PIOPS, the cost of a 1TB 3K PIOPS SSD is $425 (1,000GB * $0.125 for storage plus 3,000 PIOPS * $0.1 for operations). (EDIT: this figures are wrong; please see responses below for the right math).

EDIT: My understanding was incomplete - General Purpose SSDs can burst up to 3k IOPS, but they also provide provisioned IOPS at a rate of 3 IOPS per GB. Effectively, 1TB drive then does provide 3k PIOPS (3 * 1,000GB) and bursting limits are only a factor for smaller drives.

It looks like 3 IOPS per GB guaranteed, even when throttled, and much higher when bursting. That's still 3000 IOPS (3 X 1000) worst case for a 1TB volume.

From Jeff Barr's blog post (http://aws.amazon.com/blogs/aws/new-ssd-backed-elastic-block...):

* A bucket is associated with each General Purpose (SSD) volume, and can hold up to 5.4 million tokens.

* Tokens accumulate at a rate of 3 per configured GB per second, up to the capacity of the bucket

I take this to mean that a 1TB GP SSD gets 3K tokens/sec = consistent 3K PIOPS. Can you explain where you disagree?

Thank you for correcting me. I disagreed after reading the same blog post, but after your explanation I realised I completely missed the baseline performance guarantee. Your math was spot on!

But note that the baseline performance for the new General Purpose SSD is listed as the size (in GB) times 3 IOPS (so 3K/3072 IOPS for your 1000GB/1TB example). So large volumes will have a baseline that basically matches the listed "burst" IOPS speed, and at less than 1/2 the cost of the PIOPS version.

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