Synology SHR-2

Double-parity SHR. Survives 2 simultaneous failures while still handling mixed drive sizes. The safe Synology answer for large drives.

Min. drives
4
Usable capacity
variable
Fault tolerance
2
Performance
Like RAID 6

How it works

Like SHR-1 but with two parity drives per tier. Each tier behaves as RAID 6. Tolerates 2 simultaneous failures and a URE during rebuild. The mixed-size partition logic is identical to SHR-1.

Formula: Synology proprietary

Synology SHR-2 — tiered partitions for mixed sizesTier 2 (only on large drives)Tier 1 (across all drives)4 TB8 TB t28 TB8 TB t28 TB8 TB P8 TB4 TB t14 TB t14 TB t14 TB P
Layout diagram

Pros / Cons

Pros

  • Mixed drive sizes + double parity
  • Survives 2 drive failures
  • Tolerates 1 URE during rebuild
  • Synology-integrated
  • Migrates from SHR-1 in-place

Cons

  • Synology-only
  • Costs 2 drives of capacity
  • Less efficient on small drives — overkill if drives ≤ 4 TB
  • Variable capacity is harder to predict

When to use

Synology pools with 12 TB+ drives. 5+ bay setups. Mission-critical Synology storage.

When NOT to use

Small pools (3-4 drives, ≤ 8 TB) — SHR-1 is fine and gives you 1 more drive of capacity. 2-bay (need 4 min).

Rebuild math example

5 × 8 TB SHR-2: per tier reads (5-2) × 8 = 24 TB. At 70 MB/s ≈ 32 hours. Double parity tolerates a URE, so the rebuild survives even at NAS-class URE rates.

Check rebuild risk →

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Related

Synology SHR-1 →Synology Hybrid RAID with single parity. Partitions larger drives so every TB contributes ... RAID 6 →Block-level striping with double distributed parity (P + Q). Survives any 2 simultaneous d... ZFS RAIDZ2 →The ZFS sweet spot. Double parity, checksums, snapshots, used-block resilver. Strongly rec... Browse all RAID levels →RAID Levels
Bottom line: SHR-2 is the right Synology choice for 12 TB+ drives, 5+ bays, or critical data. The 2-drive overhead is well spent.