Disk Destroyer

There is no better tool to arrange your bits to oblivian. But if a precise cut is needed, some commands are more valuable than others. If your specific block size calculation is incorrect, you will lose your data!

RAID

Metadata information is usually at the end of the device. If you want to re-use the device, you need to wipe it out. You have the option to wait and overwrite the entire disk:

root@demo:~# dd if=/dev/zero of=/dev/sdX bs=1M status=progress

Or zero out only parts Raid controller bothers to check:

root@demo:~# DEV='/dev/sdX'; dd if=/dev/zero of=$DEV bs=512 seek=$(( $(blockdev --getsz $DEV) - 1024 )) count=1024

Software RAID and UEFI

If RAID card is not present but you need FAT for EFI boot and some redundancy:

/dev/sda1 is efi and /dev/sdb1 is empty
root@demo:~# dd if=/dev/sda1 of=/dev/sdb1
root@demo:~# mkdir /boot/efi2
root@demo:~# blkid /dev/sda1
/dev/sda1: UUID="xxxx-xxxx" TYPE="vfat" PARTUUID="xxxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx"
root@demo:~# blkid /dev/sdb1
/dev/sdb1: UUID="xxxx-xxxx" TYPE="vfat" PARTUUID="yyyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyy"
root@demo:~# cat /etc/fstab  | grep efi
PARTUUID=xxxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx  /boot/efi       vfat    umask=0077      0       1
PARTUUID=xxxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx  /boot/efi2      vfat    umask=0077      0       1
root@demo:~# efibootmgr -c -d /dev/sdb -p 1 -L "Ubuntu-AltDrv" -l '\EFI\ubuntu\shimx64.efi'

Copy block device over network

Let's assume you already have a healthy dose of SSH in your bloodstream. Copy block device /dev/sdX content from one machine to another machine /dev/sdY with the command:

root@demo:~# ssh root@source.example "dd if=/dev/sdX" bs=1M | dd of=/dev/sdY bs=1M

Swap to the resque

If you constantly get OOM killed and are happy to run your system randomly on glacier speed, then you can virtually add some RAM on the fly.
'pv' may be needed to avoid killing already slow storage. Example how to add 32G to swap:

root@demo:~# dd if=/dev/zero | pv --rate-limit 60m | dd iflag=fullblock of=/swapfile bs=1G count=32 #32G swap
root@demo:~# dd if=/dev/zero of=/swapfile bs=4k count=8388608
root@demo:~# mkswap /swapfile
root@demo:~# chmod 0600 /swapfile
root@demo:~# /sbin/swapon /var/swapfile; #'swapoff' if needed

Get CEPH backup

It is great when you have a backup or you don't destroy your network under an erasure-coded pool.

rbd export -p  pool volume-ad0ceef0-64ef-4050-afd6-3a12c13dd6be ./volume-ad0ceef0-64ef-4050-afd6-3a12c13dd6be.bac

Restore CEPH from backup

rbd rm pool volume-ad0ceef0-64ef-4050-afd6-3a12c13dd6be
rbd import ./volume-ad0ceef0-64ef-4050-afd6-3a12c13dd6be.bac  pool/volume-ad0ceef0-64ef-4050-afd6-3a12c13dd6be