wiki: add 4 new articles from archive, merge 8 archive notes into existing articles (73 articles)

New: mdadm RAID rebuild, Mastodon instance tuning, Ventoy, Fedora networking/kernel recovery.
Merged: Glacier Deep Archive into rsync, SpamAssassin into hardening checklist,
OBS captions/VLC capture into OBS setup, yt-dlp subtitles/temp fix into yt-dlp.
Updated index.md, README.md, SUMMARY.md with 21 previously missing articles.
Fixed merge conflict in index.md Recently Updated table.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

01-linux/storage/mdadm-raid-rebuild.md

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+---
+title: "mdadm — Rebuilding a RAID Array After Reinstall"
+domain: linux
+category: storage
+tags: [mdadm, raid, linux, storage, recovery, homelab]
+status: published
+created: 2026-04-02
+updated: 2026-04-02
+---
+
+# mdadm — Rebuilding a RAID Array After Reinstall
+
+If you reinstall the OS on a machine that has an existing mdadm RAID array, the array metadata is still on the disks — you just need to reassemble it. The data isn't gone unless you've overwritten the member disks.
+
+## The Short Answer
+
+```bash
+# Scan for existing arrays
+sudo mdadm --assemble --scan
+
+# Check what was found
+cat /proc/mdstat
+```
+
+If that works, your array is back. If not, you'll need to manually identify the member disks and reassemble.
+
+## Step-by-Step Recovery
+
+### 1. Identify the RAID member disks
+
+```bash
+# Show mdadm superblock info on each disk/partition
+sudo mdadm --examine /dev/sda1
+sudo mdadm --examine /dev/sdb1
+
+# Or scan all devices at once
+sudo mdadm --examine --scan
+```
+
+Look for matching `UUID` fields — disks with the same array UUID belong to the same array.
+
+### 2. Reassemble the array
+
+```bash
+# Assemble from specific devices
+sudo mdadm --assemble /dev/md0 /dev/sda1 /dev/sdb1
+
+# Or let mdadm figure it out from superblocks
+sudo mdadm --assemble --scan
+```
+
+### 3. Verify the array state
+
+```bash
+cat /proc/mdstat
+sudo mdadm --detail /dev/md0
+```
+
+You want to see `State : active` (or `active, degraded` if a disk is missing). If degraded, the array is still usable but should be rebuilt.
+
+### 4. Update mdadm.conf so it persists across reboots
+
+```bash
+# Generate the config
+sudo mdadm --detail --scan | sudo tee -a /etc/mdadm.conf
+
+# Fedora/RHEL — rebuild initramfs so the array is found at boot
+sudo dracut --force
+
+# Debian/Ubuntu — update initramfs
+sudo update-initramfs -u
+```
+
+### 5. Mount the filesystem
+
+```bash
+# Check the filesystem
+sudo fsck /dev/md0
+
+# Mount
+sudo mount /dev/md0 /mnt/raid
+
+# Add to fstab for auto-mount
+echo '/dev/md0 /mnt/raid ext4 defaults 0 2' | sudo tee -a /etc/fstab
+```
+
+## Rebuilding a Degraded Array
+
+If a disk failed or was replaced:
+
+```bash
+# Add the new disk to the existing array
+sudo mdadm --manage /dev/md0 --add /dev/sdc1
+
+# Watch the rebuild progress
+watch cat /proc/mdstat
+```
+
+Rebuild time depends on array size and disk speed. The array is usable during rebuild but with degraded performance.
+
+## Gotchas & Notes
+
+- **Don't `--create` when you mean `--assemble`.** `--create` initializes a new array and will overwrite existing superblocks. `--assemble` brings an existing array back online.
+- **Superblock versions matter.** Modern mdadm uses 1.2 superblocks by default. If the array was created with an older version, specify `--metadata=0.90` during assembly.
+- **RAID is not a backup.** mdadm protects against disk failure, not against accidental deletion, ransomware, or filesystem corruption. Pair it with rsync or Restic for actual backups.
+- **Check SMART status on all member disks** after a reinstall. If you're reassembling because a disk failed, make sure the remaining disks are healthy.
+
+Reference: [mdadm — How to rebuild RAID array after fresh install (Unix & Linux Stack Exchange)](https://unix.stackexchange.com/questions/593836/mdadm-how-to-rebuild-raid-array-after-fresh-install)
+
+## See Also
+
+- [[snapraid-mergerfs-setup]]
+- [[rsync-backup-patterns]]