Recovering Data from a Dead Synology NAS on Apple Silicon

04 Jan 2026 Comments

My Synology DS712+ decided to give up the ghost. The good news: I have a new Synology arriving tomorrow and can just pop the drives in. The bad news: I wanted to back up some data before trusting the migration process. Here’s how I mounted the drive read-only on an M1 Mac using UTM and Ubuntu.

The Challenge

Synology uses a layered storage stack:

  1. mdadm - Linux software RAID (even for single-disk setups, it uses RAID1 with one member)
  2. LVM - Logical Volume Manager on top of the RAID
  3. ext4 - The actual filesystem

macOS can’t read any of this natively, so we need a Linux VM.

Requirements

Step 1: Release the Disk from macOS

When you plug in the Synology drive, macOS will complain that it can’t read the disk. Click Eject, not Ignore. This releases the USB interface so UTM can grab it.

Quit Disk Utility if it’s open.

Step 2: USB Passthrough in UTM (The Tricky Part)

This is where I wasted the most time. On Apple Silicon with UTM, you need to attach both the disk and its USB hub/adapter.

  1. Open UTM → select your Ubuntu VM → Edit → USB
  2. Attach both devices:
    • External Disk 3.0 (the SATA drive)
    • USB-C Digital AV Multiport Adapter (or whatever hub you’re using)
  3. Start the VM
  4. Don’t hot-plug or unplug after boot

If you only attach the disk, it silently fails. Both are needed.

Step 3: Verify Linux Sees the Drive

lsblk -o NAME,SIZE,FSTYPE

You should see something like:

sdb     7.3T
├─sdb1  linux_raid_member
├─sdb2  linux_raid_member
├─sdb5  linux_raid_member
└─sdb6  linux_raid_member

If you don’t see the partitions, USB passthrough failed. Go back to step 2.

Step 4: Assemble the RAID Arrays

Here’s where I hit my first real snag. My Synology had two data partitions that needed to be assembled:

# Stop any auto-assembled arrays first
sudo mdadm --stop /dev/md126
sudo mdadm --stop /dev/md127

# Assemble both partitions as read-only RAID arrays
sudo mdadm --assemble --run --readonly /dev/md126 /dev/sdb5
sudo mdadm --assemble --run --readonly /dev/md127 /dev/sdb6

Verify they’re running:

cat /proc/mdstat

You should see both arrays listed as active (read-only).

Step 5: Activate LVM

sudo vgscan

This should find vg1000 (Synology’s default volume group name).

sudo pvscan

This is critical. You should see both /dev/md126 and /dev/md127 listed as physical volumes in vg1000. If you only see one, the LVM won’t mount correctly because half the logical volume is missing.

Now activate the volume group:

sudo vgchange -ay vg1000

Verify the logical volume is complete:

sudo dmsetup table

You should see vg1000-lv with segments pointing to real devices (like 9:126 and 9:127), not any error segments. If you see a vg1000-lv-missing_0_0 with error, you haven’t assembled all the RAID arrays.

Step 6: Mount Read-Only

sudo mkdir -p /mnt/syno
sudo mount -o ro,noload /dev/vg1000/lv /mnt/syno

The -o ro,noload flags are important:

Step 7: Browse Your Data

ls /mnt/syno

You’ll see the typical Synology layout:

@appstore
@docker
Data
docker
homes
photo
Plex
Public
surveillance
Time Machine
video

The @ prefixed directories are Synology system folders. Your data is in the others.

Copying Data Off

I used rsync to copy what I needed:

rsync -avh --progress /mnt/syno/photo/ /path/to/backup/

Everything stays read-only on the source.

Clean Shutdown

sudo umount /mnt/syno
sudo vgchange -an vg1000
sudo mdadm --stop /dev/md126
sudo mdadm --stop /dev/md127
sudo poweroff

Only unplug the disk after the VM has fully powered down.

Lessons Learned

  1. macOS Eject ≠ Ignore - You must eject the disk so UTM can claim the USB interface
  2. UTM USB passthrough requires the hub too - Attaching only the disk fails silently on Apple Silicon
  3. Synology may use multiple RAID arrays for one volume - My 7.3TB volume was split across sdb5 (2.7TB) and sdb6 (4.6TB), both as RAID1 members that LVM combined into one logical volume
  4. The noload mount option is your friend - It prevents the filesystem from replaying its journal, which would write to the disk
  5. Loop devices and offset tricks are red herrings - You can’t bypass the mdadm/LVM layers

The whole process took about an hour of trial and error, but once I understood the storage stack, it made sense. Now I can confidently migrate to the new NAS knowing my data is backed up.

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