Capacity Estimation Back Of The Envelop
| Metric System | Value |
|---|---|
| 1 Million | ${10^6}$ |
| 1 Billion | ${10^9}$ |
| 1 Trillion | $10^{12}$ |
| Data Storage Unit | Value | Byte | Byte |
|---|---|---|---|
| 1 KB | $10^{3}$ B | $10^{3}B$ | $2^{10}B$ |
| 1 MB | $10^{3}$ KB | $10^{6}B$ | $2^{10}B$ |
| 1 GB | $10^{3}$ MB | $10^{9}B$ | $2^{10}B$ |
| 1 TB | $10^{3}$ GB | $10^{12}B$ | $2^{10}B$ |
| 1 PB(PetaByte) | $10^{3}$ TB | $10^{15}B$ | $2^{10}B$ |
| 1 EB | $10^{3}$ PB | $10^{18}B$ | $2^{10}B$ |
| 1 ZB | $10^{3}$ EB | $10^{21}B$ | $2^{10}B$ |
| 1 YB | $10^{3}$ ZB | $10^{24}B$ | $2^{10}B$ |
| Two Power | Value |
|---|---|
| $2^{0}$ | 1 |
| $2^{1}$ | 2 |
| $2^{2}$ | 4 |
| $2^{3}$ | 8 |
| $2^{4}$ | 32 |
| $2^{5}$ | 64 |
| $2^{6}$ | 128 |
| $2^{7}$ | 256 |
| $2^{8}$ | 512 |
| $2^{9}$ | 1024 |
| $2^{10}$ | 2048 |
Generally for a large scale system we count as 1 Million request per day.
1 Million/day = $\frac{10^{6}}{24 hrs * 60 min * 60 sec}$ ≈ 11.57 ≈ 12Bytes/sec.
Storage Estimation/Bandwidth Estimation - Incoming(Ingress) Outgoing(Egress)
People in world = 8 billion.
People in India = 1.4 billion.
DAU Daily Active User.
MAU Monthly Active User.
Capacity Estimation Example.
Whatsapp.
DAU ≈ 2B ≈ 100B message every day.
Average message size ≈ 100 Bytes. Ask for the size and storage. Example you can assume one good image is 100Mb.
1 day of message = $100 * 10^{9} * 100$ Bytes ≈ $10^{13}$ ≈ 10TB
- 100B = 100 * $10^{9}$ Bytes
5 years of message = 10TB * 365 * 5 ≈ 20PB.
1 day of message ≈ 10TB.
Bandwidth Estimation = 10TB/day
10Tb/day ≈ 10 * $10^{6}$ * $10^{6}$ B/day
≈ 10 * $10^{6}$ * 12 B/sec
≈ 120 MB/sec.
10TB ≈ $10^{12}$ B.
$10^{6}$ B/day = 1Million/day ≈ 12/sec.
Twitter.
DAU ≈ 200M.
Read:Write ≈ 150M:100M
Storage Estimation.
- 140 char per tweet.
- 2 bytes to store char.
- 20 Bytes to store the metadata(ID, UserId, timestamp).
Total Storage for a single tweet = (140 char * 2 Bytes) + 20 Bytes metadata = 280 Bytes ≈ 300Bytes.
Write Estimates.
Daily 100M tweet. 100M * 300Bytes = 3 * $10^{10}$ B/day ≈ 30GB/day.
Every 5th tweet has a image ≈ 200 kb.
Every 10th tweet has a video ≈ 2MB/video.
Total space = $\frac{100M tweets}{5}$ * 200kb + $\frac{100 M tweets}{10}$ * 2MB
= ((20M * 200KB) + (10M * 2MB)) /day
= (20 * $10^6$ * 200 * $10^{3}$) + (10 * $10^{6}$ *2 * $10^{6}$) B/day
= (4 * $10^{12}$) + (20 * $10^{12}$) B/day
= (4TB + 20TB) /day
= 24 TB/day. (Ingress Incoming Bandwidth)
= 24 * $10^{6}$ MB/day (1TB = $10^{6}$)
= $\frac{24 * 10^{6}}{10^{5}}$ MB/sec
≈ 300 Mb/sec.
Read Estimates.
DAU = 200M.
Each people see 150 tweets.
Total size of a simple tweet = 200M * 150 tweets * 300 Bytes
= 30 * $10^{3}$ * $10^{6}$ * 300
= 9TB/day
= 9 * $10^{6}$ MB/day
= 9 * $10^{6}$ * 12 Bytes/sec
= 100 MB/sec.
Every 5th tweet contains image. $200M *150$ tweets are read daily.
Total size of the tweets contains image = $\frac{200*150}{5}$ * 200KB/day
= (6000M * 200KB)/day
= 12 * $10^{5}$ * $10^{6}$ KB/day
= 1.2 TB/day.
Every 10th tweet contains video. $200M * 150$ tweets are read daily.
Total size of the tweets contains video = $\frac{200 * 150}{10}$ * 2MB/day
= (3000M * 2MB)/day
= 6 * $10^{3}$ * $10^{6}$ * $10^{3}$ KB/day
= 6 * $10^{12}$ KB/day
= 6TB/day.
All the pics and video and text are egress requests.