Menu
RAID Made Simple: what it is and which level fits your project

RAID Made Simple: what it is and which level fits your project

Disks fail. They slow down, throw errors, or simply can’t keep up with growing load. RAID is a practical way to combine several physical drives into a single logical array to achieve the balance of speed, capacity, and fault‑tolerance your application needs. But the internet is full of lore: “RAID is a backup,” “RAID 5 is dead,” “RAID10 isn’t the same as 1+0,” and so on. This guide cuts through the noise so you can decide which RAID level fits your project on VPS or dedicated servers from Unihost-without wading into academic weeds.

What RAID actually is

RAID (Redundant Array of Independent Disks) groups multiple drives so the OS sees one volume with specific characteristics. The building blocks:

  • Striping – split data into chunks (stripes) and write them across drives in turn. Improves throughput and parallelism (e.g., RAID 0).
  • Mirroring – write each block to two or more drives. Gives fault‑tolerance and great read performance (e.g., RAID 1).
  • Parity – store extra information that lets you reconstruct data if a drive dies (e.g., RAID 5/6). A compromise of capacity vs reliability.

Important truth: RAID is not a backup. It primarily protects against drive failure. It will not save you from accidental deletes, ransomware, application bugs, or human error. Think of RAID as service continuity; think of backups as data recovery.

How it works (short and practical)

Hardware vs software RAID

  • Hardware RAID (controller card or onboard chipset): often includes cache and a BBU/supercap. Pros: fast inline performance, write‑back cache, minimal CPU use, convenient tools. Cons: dependence on the controller/firmware, trickier migrations, higher cost.
  • Software RAID (Linux mdadm, Windows Storage Spaces, BSD geom): Pros: transparent, flexible, easy to migrate, no vendor lock‑in. Cons: no dedicated hardware cache, some CPU overhead (usually modest), depends on OS tuning.

A third path: ZFS/Btrfs. These are modern filesystems with integrated redundancy (RAIDZ, mirrors) and checksums for every block to catch silent corruption (bit rot). For integrity‑critical workloads, ZFS is a standout candidate.

Key concepts you’ll meet

  • Stripe size – the chunk of data written to one disk before moving to the next. Influences performance for small vs large I/O.
  • Hot spare – an idle drive that automatically joins the array when a member fails, shortening the risk window.
  • Rebuild – the process of reconstructing redundancy after a failure. Critical factor: rebuild duration; long rebuilds increase the chance of a second failure.
  • URE (Unrecoverable Read Error) – probability of a read the controller can’t recover. On very large arrays, a single URE during rebuild can derail recovery, especially with big HDDs.

Why RAID matters

  • Service continuity: downtime of your site, database, or storage hurts revenue and reputation. RAID reduces the chance one failed drive takes you down.
  • Performance tuned to load profile: a good RAID level accelerates the operations that matter to you-sequential streams (media, backups) or random IOPS (databases, virtualization).
  • Economics: an N‑drive array can provide more usable capacity at a given fault‑tolerance than a few huge drives, and delays some scaling complexity.

RAID levels in plain English

RAID 0 – stripes, no redundancy

  • How it works: data is spread across all drives.
  • Pros: maximum speed and usable capacity.
  • Cons: any single disk failure destroys the array. Zero fault‑tolerance.
  • Use cases: scratch space, caches, ephemeral processing where data can be recreated easily.

RAID 1 – mirrors

  • How it works: every block is written to two drives (or more).
  • Pros: simple, fast random reads, tolerates a single‑disk failure.
  • Cons: 50% usable capacity with two‑disk mirrors; writes may be similar to a single disk.
  • Use cases: system volumes, critical small services, small databases where predictability and simplicity matter.

RAID 5 – stripes + single parity

  • How it works: data and one parity block are distributed across all drives; survives one disk failure.
  • Pros: good balance of capacity, reliability, and read speed.
  • Cons: write penalty for parity math; long rebuilds on big arrays; higher URE risk with large HDDs.
  • Use cases: read‑heavy workloads, moderate capacities, file shares, media archives with strong backup policies.

RAID 6 – stripes + double parity

  • How it works: like RAID 5, but with two parity blocks; survives two disk failures.
  • Pros: substantially safer than RAID 5 for big arrays.
  • Cons: higher write overhead; needs at least four drives.
  • Use cases: large HDD arrays, archives, object stores where integrity outranks write speed.

RAID 10 (1+0) – mirrors combined by striping

  • How it works: pairs of mirrors are striped together (min four drives).
  • Pros: excellent random I/O, quick degraded performance and rebuild (copy a mirror-no full parity math), strong tolerance.
  • Cons: 50% usable capacity; pricier per TB than parity arrays.
  • Use cases: OLTP databases, virtualization, high‑IO log/queue systems.

RAID 50/60 – nested parity + striping

  • How it works: stripe across multiple RAID 5 or RAID 6 groups.
  • Pros: scale‑out capacity with improved resilience vs a single RAID 5 and better load distribution.
  • Cons: more planning/monitoring complexity; parity write cost remains.
  • Use cases: large storage clusters, heavy media pipelines, backup landing zones.

JBOD – just a bunch of disks

  • What it is: no redundancy; each disk is its own volume. Not RAID, but valid when the application handles replication independently.

Performance: what really changes

  • Sequential throughput: backups, media, and analytic scans benefit from striping (RAID 0/5/6/10). More drives → higher aggregate bandwidth.
  • Random IOPS: databases and virtualization prefer RAID 10, whose mirrored pairs excel at parallel random access. RAID 5/6 pay a write penalty (read‑modify‑write cycle).
  • Latency: often lower on mirrors (RAID 1/10) and with NVMe Controllers with protected write‑back cache (BBU/supercap) can cut write latency significantly.
  • During rebuild: parity arrays (5/6) slow down more and for longer than mirrors (1/10). That matters for production SLAs.

Risks & myths (and the nuance behind them)

  • RAID ≠ backup. A dropped table or ransomware encrypts all members, instantly. Keep offsite backups and snapshots with tested restores.
  • “RAID 5 is dead.” Not universally true. With very large HDDs (10+ TB) and long rebuilds, URE risk is real; RAID 6 or RAID 10 are safer. For modest capacities with disciplined backups and monitoring, RAID 5 can still be appropriate.
  • SSD vs RAID. SSDs fail, too, and have quirks (TRIM, alignment, wear). Use matched models and monitor wear levels. On SSDs/NVMe, RAID 10 often delivers the best write behavior for databases.
  • Write‑back cache is dangerous. Only when you lack BBU/supercap and UPS. With protection, write‑back dramatically improves performance.

Choosing a RAID level for your project

1) Profile your workload

  • I/O type: sequential (media/backups) vs random (DB/VM).
  • Block sizes: large objects vs small transactions.
  • Read/write mix: 80/20 reads vs 50/50, etc.
  • Latency targets: p95/p99 expectations.

2) Define RPO/RTO requirements

  • RPO – acceptable data loss; RTO – acceptable recovery time. If RTO must be low, favor faster rebuilds (RAID 10).

3) Capacity and growth curve

  • Huge HDD pools → lean toward RAID 6 or mirrors.
  • DBs on SSD/NVMe → often RAID 10.
  • Archives/media → RAID 6/60 or ZFS RAIDZ2.

4) Controller and caching strategy

  • Hardware RAID with BBU for heavy write workloads.
  • Software RAID for flexibility and easy migrations-great on Linux (mdadm) or with ZFS.

5) Scenario‑based quick picks

  • OLTP databases (PostgreSQL/MySQL): RAID 10 on SSD/NVMe; dedicated volume for WAL/redo logs. Goal: low latency and swift rebuild.
  • Virtualization/containers (KVM/VMware/Proxmox): RAID 10 on SSD/NVMe; if capacity‑weighted with read‑heavy VMs, consider RAID 6 on HDD with SSD cache/journal.
  • File shares & media: RAID 6/60 on HDD; keep hot assets on SSD cache; strict backups; monitor rebuild impact.
  • Logs, queues, streaming: RAID 10 on SSD for high parallel small writes.
  • Backups/archives: RAID 6/60 or ZFS RAIDZ2/3; prioritize integrity and capacity over raw write speed.

Operational best practices

  • Homogeneous drives: same size/model/generation for predictable performance and rebuild behavior.
  • Hot spares: at least one spare in the array to shrink the risk window.
  • Monitor S.M.A.R.T. and controller events: temperatures, reallocated sectors, pending sectors, latency anomalies. Alert via Slack/Email/SMS.
  • Regular restore tests: a backup you’ve never restored isn’t a backup. Practice DR.
  • Alignment & stripe size: tune for your I/O profile-smaller stripes for DBs, larger for media.
  • UPS + BBU: protect write‑back caches and on‑disk consistency.
  • Avoid double caching: coordinate disk cache and controller cache policies.
  • TRIM/discard for SSDs: enable on schedule; balance against peak‑load performance.
  • Disciplined swaps: procedures for hot/cold swaps; handle trays/backplanes carefully; track serials for audit.

RAID meets modern filesystems: ZFS/Btrfs

When integrity is paramount, consider ZFS: – End‑to‑end checksums on every block, periodic scrubs, snapshots, replication, RAIDZ1/2/3 and mirrors.
– Trade‑offs: needs RAM and careful tuning.

Btrfs on Linux also offers mirrored/RAID profiles with filesystem‑level checksums. These systems shine for archives, NAS, backup repositories, and deduplicated stores.

Why Unihost

Unihost delivers configurations for any RAID story-from a simple system‑volume mirror to high‑IO RAID 10 on NVMe or capacity‑centric RAID 6/60 on HDD.

  • Right hardware: servers with PCIe Gen4/Gen5 NVMe, high‑bay HDD chassis, controllers with protected cache (BBU/supercap), and first‑class support for software RAID (mdadm/ZFS).
  • Network you can trust: private VLANs, DDoS filtering, predictable uplinks for stable rebuild windows and low latency.
  • Storage planning: help picking stripe sizes, separating logs/data, and provisioning dedicated volumes for logs/backups.
  • Automation: Terraform/Ansible templates, scheduled snapshots and offsite backups, S.M.A.R.T./controller monitoring with alerting.
  • Expertise: guidance on RAID 10 vs RAID 6 trade‑offs, reducing rebuild windows, and tuning ZFS to your profile.

Quick selection cheat‑sheet (TL;DR)

  • DBs/virtualization; IOPS & p95 matter → RAID 10 on SSD/NVMe.
  • Archive/media; capacity & reads matter → RAID 6/60 on HDD with SSD cache.
  • Backups; integrity first → ZFS RAIDZ2/3 or RAID 6 + regular scrubs/checks.
  • System volume; simplicity → RAID 1
  • Ephemeral/test/caches → RAID 0 (only with easy rebuilds and real backups).

Conclusion & CTA

RAID isn’t a buzzword or a silver bullet. It’s a pragmatic tool that, when matched to your workload, reduces downtime risk, boosts performance, and simplifies operations for SRE/DevOps teams. The secret is to map your I/O profile to the strengths of each RAID level, keep real backups and observability in place, and plan for rebuild reality-not just lab numbers.

If you want a confident start, the Unihost team will help you choose servers, drives, and controllers; assemble and benchmark the array; wire up monitoring; and train your team on runbooks.

Try Unihost servers – stable infrastructure for your projects.
Order a dedicated server on Unihost with the RAID profile you need and get the right mix of speed, capacity, and resilience-without compromise.