View source for Linux software raid

Linux software raid is done via the '''mdraid''' package.

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=== Fix on reboot ===

This shit is just horrible.  It won't restart on reboot.  I need to take time to fix all this shittiness... but for now this got me running after reboot:
 sudo su -
 mdadm --assemble --scan
 # ^ first time, this gave me errors in config, because the array line was in there twice
 # I removed ONE of the lines, and reran...
 mdadm --assemble --scan
 
    mdadm: /dev/md/0 has been started with 2 drives.
 
 mount /spiceflow/softraid

=== Install ===

mdraid has not received the polish it needs to Just Work. It has serious flaws that after hours of learning, still leave you unsure and hanging and most likely bailing out of the entire process. But it is the best thing we have on the planet, so let’s distill it down to the essentials.
* check S.M.A.R.T. data of drives – run tests and make sure they are completely healthy!
* clean raid drives of superblock and partition data
    mdadm --misc --zero-superblock /dev/sdd && dd if=/dev/zero of=/dev/sdd bs=1M count=100 && mdadm --examine /dev/sdd
     mdadm: No md superblock detected on /dev/sdd.
* use whole drives (not drive partitions) in a newly created raid
    mdadm --create --verbose /dev/md0 --level=mirror --raid-devices=2 /dev/sdd /dev/sde 
     mdadm: size set to 3906887488K 
     mdadm: automatically enabling write-intent bitmap on large array 
     Continue creating array? yes 
     mdadm: Defaulting to version 1.2 metadata 
     mdadm: array /dev/md0 started.
    watch -n 1 cat /proc/mdstat
    # wait 400 FUCKING MINUTES for a GODDAMNED EMPTY 4TB DRIVE to sync with ANOTHER empty 4TB drive, FUCKSAKE
    # IF YOU REBOOT BEFORE THAT, IT WILL BE AS IF YOU NEVER SET UP A RAID
* save and reboot and make sure the mdraid service restores the raid
    mdadm --detail --scan >>/etc/mdadm.conf 
    rc-update add mdraid boot
    # start then stop then start the /etc/init.d/mdraid service, make sure this works to restore your raid (check /proc/mdstat) 
    # format /dev/md0 as ext4 and set up an auto mount point in /etc/fstab 
    # reboot and pray
* hopefully much later, upon failure, to restore a single drive, set it up as a raid:
    madadm -A /dev/sdd # I THINK! it's all very iffy. Which SUCKS.

=== Monitor ===

RAID is no use if you don't monitor it!  So... monitor it!  The horribleness of mdadm is confirmed again [https://raid.wiki.kernel.org/index.php/Monitoring_your_system  here in these monitoring notes].  Do this on occasion:

 # GREAT simple status of any raids
 # bitpost should show: md0 : active raid1 sdd[0] sde[1]
 cat /proc/mdstat    
 
 # drive health
 sudo smartctl /dev/sdd -a
 sudo smartctl /dev/sde -a
 
 # this is supposed to maybe email you on monitoring events... i'll believe it when i get one... 
 # there's no way email works... and that notes page warns that it may just silently die on you...
 # sigh
 sudo mdadm -F -s --mail m@bitpost.com

Also try the stuff [[Check disk|here]].

=== Pray ===

Honestly, you should spend more time on this... before you have to...