Can I change RAID type without losing data?

Some RAID changes can be done in place without losing data; others require a rebuild from backup. Which is which depends on the source and target types and your NAS platform.

Migrations that are typically supported

Synology allows several non-destructive migrations, generally by adding drives rather than reformatting:

• RAID 1 → RAID 5 (add a drive).
• RAID 5 → RAID 6 (add a drive), and SHR → SHR-2.
• Expanding an existing array by adding drives or replacing with larger ones.

These run in the background while the volume stays online, though performance dips during the migration.

Changes that usually require a rebuild

Going the other direction (e.g. reducing redundancy), or converting between fundamentally different layouts that the system does not support live, means back up, delete the pool, recreate it in the new type, and restore. Check your exact source-and-target combination against Synology's documentation before starting — the supported matrix varies by model and DSM version.

The rule that never changes

Whatever the migration, have a current, verified backup first. Even a supported in-place migration stresses the drives and is not risk-free — a drive failing mid-migration on an array with thin redundancy can be costly. If you are adding drives for the migration, use CMR NAS drives; the table lists options.