RAID Reconstruction Basics
RAID presents storage assembled from multiple members, but the mapping depends on the level: mirroring duplicates data, striping distributes it, and parity layouts add calculated redundancy. Recovery reconstructs the relevant virtual address space and array state well enough to expose the structures above it. A controller rebuild is write-capable; recovery software can usually assemble a candidate RAID virtually and verify it first.
Start with the member set
Identify every original member, replacement disk, hot spare and disk that may have been removed earlier. Labels and slot numbers help, but metadata, serial numbers, logs and data patterns may be needed to establish the relevant array state.
The layout is more than disk order
Depending on RAID level and implementation, reconstruction may require member order, data offset, stripe/chunk size and, for parity arrays, parity placement/rotation and layout rules. Nested arrays add another geometry layer; some controllers or appliances add metadata or transformations of their own. On-disk metadata can supply much of this, but it still has to represent the array state being recovered.
Missing and stale members are different
A disk can be absent, unreadable, partially rebuilt, or simply older than the other members. Treating a stale disk as current can be worse than treating it as missing because its sectors look valid while representing an earlier state.
Verify before writing
A candidate virtual RAID should be checked at more than one location: expected partition/volume structures, coherent file-system metadata, directory trees and representative files should agree across the address space. A successful mount or readable directory near the beginning is not enough to prove member order or parity geometry. Physical rebuild is a separate maintenance decision after the recoverable state is understood.
Reconstruction answers “how were these members combined?” A rebuild writes calculated data back into an array. In uncertain cases, answer the first question before doing the second.
Related: RAID Array Failure · Failed RAID Rebuild · NAS Failure