Storage Redundancy and Failover Techniques on Bare Metal

When you're working in the cloud, redundancy is often abstracted away. You assume the disk will be replicated, the VM will restart, and someone else is making sure your data lives in three different zones. But on bare metal? You're the one holding the bag when a drive fails at 2 a.m.

That's why building proper storage redundancy isn't just about data safety — it's about keeping your system online, restorable, and recoverable without drama. The goal here isn't perfection — it's survivability.

What Redundancy Really Means

Let's clear something up: redundancy doesn't just mean “I have a RAID array.” It means your system can keep functioning — or quickly recover — when a component fails. That includes:

• A drive failure that doesn't bring the system down.
• A degraded node that doesn't break the whole application.
• A planned maintenance window that doesn't take production offline.
• A data corruption event that can be rolled back with confidence.

It's not just about hardware mirroring — it's about building storage patterns that let you respond to failure without scrambling.

RAID Still Has a Place — Just Know Its Limits

RAID has been around for decades, and it still serves a useful purpose — especially when you're managing your own disks directly. But it's not a magic bullet. The choice between local storage and network-attached storage plays a crucial role in your redundancy strategy.

RAID 1 and RAID 10 are the go-to for fast reads and mirrored redundancy. You lose capacity, but gain resilience and speed — and rebuilds are relatively quick.

RAID 5 and RAID 6 offer better capacity usage, but they come with caveats: slower writes, longer rebuild times, and a dangerous window during recovery where another disk failure can mean data loss.

ZFS-based RAID (RAID-Z, RAID-Z2, RAID-Z3) adds data checksumming and self-healing — a major upgrade if you're concerned about silent corruption. But it comes with resource costs (RAM, CPU), and you need to treat ZFS like a storage stack, not just a file system.

And then there's the age-old debate: hardware RAID vs software RAID. Hardware RAID can offload CPU work, but makes it harder to move arrays between systems. Software RAID (e.g. `mdadm`) is more transparent and flexible — especially in environments where automation matters.

The key takeaway? RAID protects against drive failure — but it doesn't help if your whole server dies, your file system gets corrupted, or you accidentally delete something.

Real Redundancy Lives Beyond RAID

RAID helps, but real resilience often means going one layer up — thinking across hosts and designing for actual failover.

Here are some proven approaches:

ZFS Send/Receive Replication

If you're using ZFS, you can stream filesystem snapshots across machines with `zfs send | ssh zfs receive`. It's incredibly effective for near-real-time replication with built-in consistency. Great for warm failover setups or staging environments that track prod.

rsync + Snapshots

A classic for a reason. Use `rsync` on a cron job or watch service to copy changed files between hosts, and pair it with LVM or Btrfs snapshots for consistent recovery points. It's low-complexity and doesn't require a new storage layer — just smart scripting.

DRBD (Distributed Replicated Block Device)

Think of DRBD like RAID-1 over the network. It mirrors block devices between servers, so if one node dies, the other can mount and continue. It's mature, stable, and great for HA pairs. Just be sure you have split-brain protection and fencing configured. This approach works well with both SATA and NVMe drives, though performance characteristics differ.

GlusterFS and Ceph

These are full-blown distributed storage platforms. They provide shared volumes with replication, healing, and failover — and they scale well. But they also add operational overhead. If you don't have a team ready to support them, they can be more pain than protection.

And remember: backups are not redundancy. Backups help you roll back from data loss. Redundancy keeps things running through a failure. You need both — but they're not the same job.

Don't Just Build for Uptime — Build for Recovery

Sometimes you don't need full HA. You just need a system that's easy to fix when things go sideways.

That means asking questions like:

• If a server fails, how fast can I provision a replacement?
• Are my mounts and configs designed to reconnect automatically?
• Can my app restart cleanly after a volume switch or failover?
• Do I have alerts that trigger before performance collapses?

A resilient system isn't one that never fails. It's one that fails gracefully and predictably — and comes back online without heroics.