Explain like I'm five · Database

What is RAID?

RAID, told as a story about splitting goods across several shelves — or doubling them up — to be faster and safer than a single shelf.

with every box on one shelf, pulling boxes out is slowand if that shelf breaks, every box is gone

With every box on one shelf, pulling boxes out is slow.And if that shelf breaks, every box is gone.

splitting boxes across slots speeds up pulling them, but one broken slot ruins all the data

Splitting boxes across slots speeds up pulling them, but one broken slot ruins all the data.Pulling boxes got faster, but the data got less safe.

split (striping)double up (mirroring)RAID = combining several shelves (disks): split for speed, doubled for safetyseveral shelves work together as if they were one

RAID splits and doubles boxes across several shelves (disks), making storage faster and safer than one shelf.Several shelves work together as if they were one.

Split it upfast, but one failure loses it all (RAID 0)
Double it upsafe, but half the capacity (RAID 1)
Add one checksum slotsplit plus a checksum to rebuild (RAID 5)
Both split and doubledfast and safe together (RAID 10)
RAID 0fast, no recoveryRAID 1safe, half capacityRAID 5split + one checksum slotRAID 10both split and doubledthe key point is how each level trades speed, safety, and capacityon RAID 1, 5, and 10, surviving shelves and a spare (hot spare) rebuild a failed slot

Each level trades off speed, safety, and capacity differently.On RAID 1, 5, and 10, data on the surviving shelves can rebuild a failed slot.

RAID's copy sits inside the same warehousea copy kept somewhere else is the real backupif the whole warehouse burns, the doubled shelf burns too

RAID is not a backup.If the whole warehouse burns, the doubled shelf burns too.

In one breath

RAID combines several disks, splitting data across them (striping) or duplicating it (mirroring), to beat a single disk on speed, safety, or both.

RAID 0 trades purely for speed, RAID 1 purely for safety, RAID 5 splits data with distributed parity for a middle ground, and RAID 10 combines striping and mirroring for both. But RAID is only redundancy among disks in the same location — it doesn't protect against fire, theft, or accidental deletion. A separate, off-site backup is still required.

When grown-ups say it

Striping
Splitting goods across several shelves. Fast, but one failed disk loses all the data.
Mirroring
Stacking an identical copy alongside. Half the usable capacity, but safe.
Parity
A checksum slot that, with the surviving slots, rebuilds a failed one. Lets you recover even if one slot fails.
RAID 5
Striping plus one parity slot. A middle ground on speed and capacity.
RAID 10
Both striped and mirrored. Keeps both speed and safety.
Hot Spare
A spare shelf waiting on standby. Steps in immediately when a shelf fails.
Difference from Backup
RAID is only a copy inside the same warehouse. Real disaster protection needs an off-site backup. → the box kept somewhere else
Fault Tolerance
The system keeps working even if some disks fail. One of the goals RAID is built for.
Next story
The Tidied Warehouse vs. the Raw Storage Yard →
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