Clone Fusion Drive

[GP-SE]

Hey guys, how do I clone just the mechanical hard drive in my fusion drive setup:
128GB SSD
1TB Hard Drive

I just want to clone the mechanical hard drive, so I can replace it with another one (same 1TB size, just different brand)

I know on Windows I can do a block level copy of the hard drive using acronis software, but does the same thing exist on the mac?

 

[satcomer]

What are you using to clone the drive?

 

[ScoobyMcDoo]

You might be able to use the dd command:

dd bs=500m if=/dev/rdiskx of-/dev/rdisky

Where x and x are numbers indicating the correct disk device. You will have to figure out what these are. The bs (block size) argument I put in the example may not be optimal. Usually the larger you use, the faster it will run as long as you don't make the buffer so big that it gets paged out.

Use the man command to get full documentation on the dd command.

 

[Weaselboy]

Hey guys, how do I clone just the mechanical hard drive in my fusion drive setup:
128GB SSD
1TB Hard Drive

I just want to clone the mechanical hard drive, so I can replace it with another one (same 1TB size, just different brand)

I know on Windows I can do a block level copy of the hard drive using acronis software, but does the same thing exist on the mac?

I don't believe any utility is going to be able to do what you want since a Fusion drive is seen by the system as one, large drive. You are going to need to copy everything off the Fusion drive then replace the HDD and recreate the Fusion drive and copy your data back to the Fusion.

 

[gandalf239]

If we're just talking about the physical drives, would it be possible to take (theoretically) a failing SDD out of an iMac with Fusion Drive, put it in adapter of some sort, clone it to a similar SSD using dd, put the new SSD in the iMac, without splitting the fusion drive? It seems this is at least theoretically possible, but I don't know enough about how fusion and/or APFS work to know if there are other variables I'm not considering. Yes, it's pretty darn inconvenient tearing down an iMac; so, yes, it would be way more convenient to clone the entire fused drive to a single, new capacious drive and all... I just want to know if what I'm proposing here is within the realm of possibility?

 

[indiekiduk]

As an experiment I tried to clone just the SSD cache part of an APFS fusion drive using dd and did newfs_hfs on the source disk0s3 (diskutil doesn't allow formatting partitions that are apfs) then reboot although it didn't work the first time with target partition initially as JHS+, I tried again with the target partition formatted as APFS (previously I had it jhfs+) and after a reboot it worked! And the files are even intact.

Before:

/dev/disk6 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +14.0 TB    disk6
                                 Physical Stores disk5s2, disk0s3
   1:                APFS Volume Untitled                1.4 MB     disk6s1

Clone source physical store disk0s3 to target disk4s2:

admin@Mac-mini ~ % sudo dd bs=500M if=/dev/disk0s3 of=/dev/disk4s2 status=progress
  19922944000 bytes (20 GB, 19 GiB) transferred 74.066s, 269 MB/s   
38+1 records in
38+1 records out
20134215680 bytes transferred in 74.775012 secs (269263958 bytes/sec)

Wipe source to stop it interfering:

admin@Mac-mini ~ % sudo newfs_hfs -J -v "Untitled" disk0s3
Initialized /dev/rdisk0s3 as a 19 GB case-insensitive HFS Plus volume with a 8192k journal

After reboot:

/dev/disk6 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +14.0 TB    disk6
                                 Physical Stores disk4s2, disk5s2
   1:                APFS Volume Untitled                1.4 MB     disk6s1

Note change in Physical Stores.