AWS RDS Provisioned IOPS really worth it?

62
votes

As I understand it, RDS Provisioned IOPS is quite expensive compared to standard I/O rate.

In Tokyo region, P-IOPS rate is 0.15$/GB, 0.12$/IOP for standard deployment. (Double the price for Multi-AZ deployment...)

For P-IOPS, the minimum required storage is 100GB, IOP is 1000. Therefore, starting cost for P-IOPS is 135$ excluding instance pricing.

For my case, using P-IOPS costs about 100X more than using standard I/O rate.

This may be a very subjective question, but please give some opinion.

In the most optimized database for RDS P-IOPS, would the performance be worth the price?

or

The AWS site gives some insights on how P-IOPS can benefit the performance. Is there any actual benchmark?

SELF ANSWER

In addition to the answer that zeroSkillz wrote, I did some more research. However, please note that I am not an expert on reading database benchmarks. Also, the benchmark and the answer was based on EBS.

According to an article written by "Rodrigo Campos", the performance does actually improve significantly.

From 1000 IOPS to 2000 IOPS, the read/write(including random read/write) performance doubles. From what zeroSkillz said, the standard EBS block provices about 100 IOPS. Imagine the improvement on performance when 100 IOPS goes up to 1000 IOPS(which is the minimum IOPS for P-IOPS deployment).

Conclusion

According to the benchmark, the performance/price seems reasonable. For performance critical situations, I guess some people or companies should choose P-IOPS even when they are charged 100X more.

However, if I were a financial consultant in a small or medium business, I would just scale-up(as in CPU, memory) on my RDS instances gradually until the performance/price matches P-IOPS.

2
performanceamazon-web-servicesamazon-rds
Note that Amazon introduced SSD-backed EBS after this question was asked. SSD-backed EBS has a significantly lower cost per OPS, making it much harder to justify PIOPs. Of course, PIOPs has a max performance of 4000 OPS rather than 3000 offered by SSD (or 40-200 offered by magnetic). – Brian
Of course, Amazon intermittently improves the performance caps on these options. See aws.amazon.com/ebs/details/#VolumeTypes for up to date metrics. – Brian

2 Answers

37
votes

Ok. This is a bad question because it doesn't mention the size of the allocated storage or any other details of the setup. We use RDS and it has its pluses and minuses. First- you can't use an ephemeral storage device with RDS. You cant even access the storage device directly when using the RDS service.

That being said - the storage medium for RDS is presumed to be based on a variant of EBS from amazon. Performance for standard IOPS depends on the size of the volume and there are many sources stating that above 100GB storage they start to "stripe" EBS volumes. This provides better average case data access both on read and write.

We run currently about 300GB of storage allocation and can get 2k write IOP and 1k IOP about 85% of the time over a several hour time period. We use datadog to log this so we can actually see. We've seen bursts of up to 4k write IOPs, but nothing sustained like that.

The main symptom we see from an application side is lock contention if the IOPS for writing is not enough. The number and frequency you get of these in your application logs will give you symptoms for exhausting the IOPS of standard RDS. You can also use a service like datadog to monitor the IOPS.

The problem with provisioned IOPS is they assume steady state volumes of writes / reads in order to be cost effective. This is almost never a realistic use case and is the reason Amazon started cloud services to fix. The only assurance you get with P-IOPS is that you'll get a max throughput capability reserved. If don't use it, you pay for it still.

If you're ok with running replicas, we recommend running a read-only replica as a NON-RDS instance, and putting it on a regular EC2 instance. You can get better read-IOPS at a much cheaper price by managing the replica yourself. We even setup replicas outside AWS using stunnel and put SSD drives as the primary block device and we get ridiculous read speeds for our reporting systems - literally 100 times faster than we get from RDS.

I hope this helps give some real world details. In short, in my opinion - unless you must ensure a certain level of throughput capability (or your application will fail) on a constant basis (or at any given point) there are better alternatives to provisioned-IOPS including read-write splitting with read-replicas memcache etc.

34
votes

So, I just got off of a call with an Amazon System Engineer, and he had some interesting insights related to this question. (ie. this is 2nd hand knowledge.)

standard EBS blocks can handle bursty traffic well, but eventually it will taper off to about 100 iops. There were several alternatives that this engineer suggested.

  1. some customers use multiple small EBS blocks and stripe them. This will improve IOPS, and be the most cost effective. You don't need to worry about mirroring because EBS is mirrored behind the scenes.

  2. some customers use the ephemeral storage on the EC2 instance. (or RDS instance) and have multiple slaves to "ensure" durabilty. The ephemeral storage is local storage and much faster than EBS. You can even use SSD provisioned EC2 instances.

  3. some customers will configure the master to use provisioned IOPS, or SSD ephemeral storage, then use standard EBS storage for the slave(s). Expected performance is good, but failover performance is degraded (but still available)

anyway, If you decide to use any of these strategies, I would recheck with amazon to make sure I haven't forgotten any important steps. As I said before, this is 2nd hand knowledge.