Can you help me understand "Free Storage Space" for RDS?


I see in my RDS dashboard monitoring, that my "Free Storage Space" is 17GB (out of 20GB).

But I recently get a warning email that says: "Your account has exceeded 85% of the usage limit"

Product --- AWS Free Tier Usage as of 01/27/2023 --- Usage Limit --- AWS Free Tier Usage Limit

AmazonRDS --- 17.0698922 GB-Mo --- 20 GB-Mo --- 20.0 GB-Mo for free for 12 months as part of AWS Free Usage Tier (Global-RDS:StorageUsage)

So which is it? is my usage 17gb? or is my free space 17gb?

1 Answer

That's a normal warning towards the end of the month if you're using the max allowable under the free tier. You have a 20GB disk that will, by definition, use 20 GB-Mo of storage allowance in 1 month, which is exactly what's allowed under free tier. At the start of the month you will have used 0 GB-Mo, and you use a bit each day. 85% of the way through the month you will have used 85% of 20 GB-Mo so the warning gets triggered.

answered a year ago
  • Thanks for clarifying. This coincidence of having 17GB free space and 17GB being 85% of my 20GB really confused me. I understand hours being incremented as the month goes by, but how is storage incremented towards the end of the month, its hard to wrap my head around this...

  • Storage is charged by "capacity x time" i.e. "GB x Months", so the longer you use it the more you pay. If you use 20GB for 1 month you're charged 20 x 1 GB-Mo. If you use 20GB for 85% of a month then you're charged 20 x 0.85 GB-Mo.

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