The disk that died on Monday
A small design firm keeps all its client work on one disk. On Monday morning the disk makes a clicking noise and stops. Ten people cannot work.
Now picture the same firm with two disks that hold the same work. One dies. Nobody notices. That idea has a name, and you will learn it today.
Key words
| Word | What it means | Example |
|---|---|---|
| RAID | several disks working together as one store | |
| Mirroring | writing the same data to two disks | RAID 1 |
| Striping | splitting data into pieces across several disks | |
| Parity | extra check data that can rebuild a lost piece | |
| NAS | network attached storage: a box of disks that shares files over a network | |
| SAN | storage area network: a fast private network that links servers to big storage | |
| Network | computers joined together so they can share things | |
| Redundancy | spare copies or parts so one failure does not stop work |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can describe RAID 1, 5 and 10, and say when to use a NAS or a SAN.
Starter
Have a go
Starter
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
RAID joins disks to survive a failure
RAID joins several disks so they work as one. There are two big ideas. Mirroring writes the same data to two disks. Striping splits data into pieces across disks, which is faster.
Parity is extra check data. If a disk dies, the parity and the other disks can rebuild what was lost. All this is redundancy: spare copies so a failure does not stop work.
RAID 1, RAID 5 and RAID 10
| Level | Disks needed | How it works | Space you can use | Survives |
|---|---|---|---|---|
| RAID 1 | 2 | Mirror: both disks hold the same data | One disk | One disk failing |
| RAID 5 | 3 or more | Data and parity spread over all disks | All disks but one | One disk failing |
| RAID 10 | 4 or more | Pairs of mirrored disks, striped together | Half the disks | One failure in each pair |
The cells students fill in are left blank in this preview.
Worked example: space on 2 TB disks
| Level | Disks | Size of one disk | Space you can use |
|---|---|---|---|
| RAID 1 | 2 | 2 TB | 2 TB |
| RAID 5 | 4 | 2 TB | 6 TB |
| RAID 10 | 4 | 2 TB | 4 TB |
The cells students fill in are left blank in this preview.
Check
Have a go
Check
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.