Outcome
By the end of this lesson, you will be able to tell disks, object storage and snapshots apart and say how each one is charged.
| Prerequisites | L1 |
| Time | 8 minutes |
1. Concept
Storage is space for keeping data. Files, photos, database records, backups: anything that needs to still be there tomorrow.
Storage is measured in gigabytes (GB). One gigabyte holds roughly a few hundred phone photos. A terabyte (TB) is about a thousand gigabytes.
The cloud offers storage in a few shapes. Three matter for a beginner.
Disks: storage plugged into a machine
A VM needs a disk to hold its operating system and files, just as a laptop has a hard drive. In the cloud that disk is a separate thing you rent, attached to the VM over the provider’s network. This kind of storage is called block storage.
- AWS calls them EBS volumes.
- Google Cloud calls them Persistent Disks.
- Azure calls them Managed Disks.
The key point: a disk is usually charged on the size you asked for, not on how full it is. Rent a 500 GB disk and put 20 GB on it, and you pay for 500 GB. It is like renting a storage unit: the price depends on the size of the unit, not on how many boxes are inside.
The disk is also separate from the machine. Stop the VM and the disk keeps its data, so it keeps charging. Delete the VM and, depending on settings, the disk may stay behind and keep charging too.
Object storage: a huge filing cabinet
Object storage is for files that do not need to be attached to a particular machine: images on a website, backups, exports, logs. You put a file in and get it back by name, from anywhere with permission.
- AWS calls it S3.
- Google Cloud calls it Cloud Storage.
- Azure calls it Blob Storage.
Object storage is charged on what you actually store, measured in GB per month, plus a tiny charge for each request to read or write a file. It also comes in tiers. Colder tiers, meant for data you rarely touch, are cheaper to keep but cost more to read back, and some charge a minimum stay of weeks or months.
Snapshots: a photo of a disk
A snapshot is a copy of a disk saved at one moment in time, like taking a photo of it. Teams take snapshots as backups before changes, or every night on a schedule. Each snapshot is charged per GB per month for as long as it is kept. Nightly snapshots that are never deleted pile up quietly.
What the meter counts
All three are priced in GB-months: one gigabyte kept for one month. Keep 100 GB for a month and you pay for 100 GB-months. The meter runs whether or not anyone reads the data.
2. Worked example
A team’s storage for one month. Prices are illustrative.
| Item | Size charged | Illustrative rate | Monthly cost |
|---|---|---|---|
| Disk on the website VM (500 GB rented, 20 GB used) | 500 GB | $0.10 per GB-month | $50 |
| Object storage for website images | 200 GB | $0.02 per GB-month | $4 |
| 30 nightly snapshots, about 20 GB each | 600 GB | $0.05 per GB-month | $30 |
| Old archive in a cold tier | 1,000 GB | $0.004 per GB-month | $4 |
Three things stand out. The disk costs most, mostly for empty space. The snapshots cost more than the website images, because nobody set a rule to delete old ones. And a whole terabyte of rarely used data costs very little in a cold tier, so long as nobody needs to read it back often.
(Snapshots usually only store the parts of a disk that changed, so real snapshot sizes are often smaller. The round numbers here keep the sum simple.)
3. Hands-on (5 min: no account needed)
1. Open the Amazon S3 pricing page: aws.amazon.com/s3/pricing2. Find the price per GB per month for "S3 Standard" in any region.3. Find the price per GB per month for one of the "Glacier" tiers.4. Work out the monthly cost of keeping 1,000 GB in each.5. Scroll to the request and retrieval prices for the Glacier tier and note that reading data back has its own charge.You should see the cold tier cost a small fraction of the standard tier to keep. That is the trade: cheap to store, slower and dearer to get back. Google Cloud Storage and Azure Blob Storage pricing pages show the same pattern under different tier names.
4. Knowledge check
Q1
A team rents a 1,000 GB disk and stores 50 GB on it. What are they usually charged for?
A. 50 GB, the space actually filled
B. Nothing, until the disk is more than half full
C. 1,000 GB, the size of the disk they asked for
D. 500 GB, an average the provider works out
Show answer
Correct: C. Disks are usually charged on the size provisioned, like a storage unit charged by its size, not by how many boxes are in it. Object storage is the one charged on what you actually store.
Q2
A VM is stopped. What happens to the charge for its disk?
A. It keeps charging, because the disk still holds the data
B. It stops, because the disk is part of the machine
C. It halves until the VM is started again
D. It moves to a cheaper cold tier automatically
Show answer
Correct: A. The disk is a separate rented item. Stopping the machine stops compute, but the disk keeps the data and keeps its meter running. Nothing moves it to a cheaper tier on its own.
Q3
What is a snapshot?
A. A small, fast disk used for temporary files
B. A copy of a disk saved at one moment in time
C. A report showing what a disk cost last month
D. A cheaper tier of object storage for old files
Show answer
Correct: B. A snapshot is a point-in-time copy of a disk, used as a backup, and it is charged per GB-month for as long as it is kept. It is not a report or a storage tier.
5. Apply
When you see a storage line on a bill, ask what shape it is. A disk? Check its size against what is on it. Object storage? Check which tier it is in. Snapshots? Check how old the oldest one is and whether anyone still needs it. Storage rarely spikes; it grows slowly, which is exactly why it goes unnoticed.