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Hello, good morning. :)

I got some questions about the RAID 2, 3, and 4:
1. In RAID 2 and 3, if the parity disk is damage can I still recover the files?
2. In RAID 4, if the ECC disk is damage can I still recover the files?

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For — short practical answer: in most real-world implementations of RAID 2, 3 and 4 a failed parity/ECC disk does not immediately make the user data unreadable. The array becomes degraded (no redundancy) but reads usually still work and you can rebuild the parity/ECC by replacing the failed disk and letting the controller/software recompute parity. That said, a degraded array is vulnerable: a second disk failure or an unrecoverable read error during rebuild can cause data loss.

RAID 2 specifics: RAID 2 uses bit-level striping with Hamming-code ECC spread across multiple disks. It was intended to correct single-bit errors; recovery depends on the ECC capability and on how many disks have failed. RAID 2 is largely historical and rarely encountered in modern systems. (See RAID 2 for details.)

RAID 3 and RAID 4 specifics: both use a dedicated parity disk (parity per stripe or per block). Parity is typically the XOR of the corresponding data blocks; if the parity disk fails you can reconstruct parity from the remaining data disks by XOR-ing them onto a replacement. While the array is degraded you have no tolerance for another disk failure. For larger disks/arrays consider RAID 6 (double parity) to reduce rebuild risk.

Immediate practical steps (general guidance):

  • Avoid writes; if possible mount read-only or pause services.
  • Check controller/OS array status and identify the failed device.
  • Inspect drive health (e.g. smartctl -a /dev/sdX).
  • Replace the failed disk with an equal-or-larger drive and trigger the rebuild using your vendor tool or mdadm on Linux: 
mdadm --detail /dev/md0
mdadm --manage /dev/md0 --add /dev/sdX

Do not reinitialize the array or blindly zero drives. Back up critical data first, monitor the rebuild, and consider moving to distributed or dual-parity RAID (RAID 5/6) and regular backups to reduce future risk. References: RAID 2, RAID 3, RAID 4, RAID 6, and the mdadm manual.

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Member Avatar for SHENGTON

Anyone?

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The answer is yes! There is only one RAID configuration in which a single disk failure causes all data loss... striping without parity or mirroring (RAID 0).

It may be better to talk about the purpose for the RAID set. The only time I would employ RAID 0 is for something like a gaming computer where data loss is not a big deal, but performance is.

Member Avatar for SHENGTON

Thanks for replying my queries techsheaven.

I forgot to include this question. What does the Parity Bit do in RAID?

Edited by SHENGTON because: n/a
Member Avatar for techsheaven

Error detection and correction. This is different from the parity block (the actual data).

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