Using ldmtool to mount NTFS dynamic mirror

How to do a read-only automatic fstab mount of an NTFS dynamic mirrored volume in Linux:

Add ldm service to automatically create /dev/mapper for dynamic volumes

sudo vim /etc/systemd/system/ldm.service

[Unit]
Description=ldmtool
After=network.target

[Service]
Type=forking
User=root
ExecStart=/usr/bin/ldmtool create all
Restart=on-failure

[Install]
WantedBy=multi-user.target

Now you need to reboot

systemctl reboot

Automatic mounting

Find the UUID of the dynamic volume using ldmtool

sudo ldmtool scan

Find the dev mapper ID of the volume, it should be dm-uuid-LDM-Volume1-LDM_UUID_GOES_HERE, where the UUID should be the same as the one we already identified, might as well double check though

cd /dev/disk/by-id/
ls -alF

Create mount directory

sudo mkdir /var/mnt/whatever

Add to /etc/fstab to mount readonly

sudo vim /etc/fstab

/dev/disk/by-id/dm-uuid-LDM-Volume1-LDM_UUID_GOES_HERE /var/mnt/whatever ntfs defaults,ro,nofail 0 0

Test mount to make sure it's valid

sudo mount -a

If it's valid then it should be remounted upon reboot due to fstab entry

Stop the subportions of the array from appearing in udisks drive list

If you don't do this then the volume subparts get listed in any program that asks udisks for a list of disks. Dolphin, LibreOffice, possibly other tools. Clicking them tries to mount the individual volume subportion which is undesired and might cause corruption of the array. It seems safer to create a udev rule which blocks the subparts from appearing in the udisks drive list, so they don't appear on the GUI anywhere.

Find the UUID of the NTFS volume using lsblk

lsblk -f

Create hide partition udev rules file, replace the IDs as appropriate

sudo vim /etc/udev/rules.d/99-hide-partitions.rules

SUBSYSTEM=="block", ENV{ID_FS_UUID}=="NTFS_UUID_GOES_HERE", ENV{UDISKS_IGNORE}="1"
SUBSYSTEM=="block", ENV{DM_UUID}=="LDM-Volume1-LDM_UUID_GOES_HERE", ENV{UDISKS_IGNORE}="0"

Important: do not add volume into fstab by NTFS UUID

If ldmtool does run, the UUID of the NTFS volume is pointed at the ldm /dev/mapper/ which works, so sometimes people do this.

However, if ldmtool doesn't run for some reason, the UUID link of the NTFS UUID instead points at one of the volume subparts. This would result in Linux trying to mount that subpart instead, which might result in corruption of the array. Using the LDM volume ID as documented above is much safer and results in the mount silently failing if ldmtool fails to run rather than the volume potentially being corrupted.

Known issues

• Dolphin shows unmount icon against LDM volumes for some reason (not sure how to fix this)