Disk4s1

[Ling Baus]

When you plug a disk into a mac the OS it gives it an identifier, disk4s1 for example as you have, this is not unique to that disk, so if you were to eject that disk and insert another the mac will probably give it the identifier disk4s1.

Last week, I bought a new WD drive and tried to mount it. Yes I tried to click on Erase, and format it with a GUID Partition Map. Guess what, the new WD drive suddenly disappeared, as the Mac tells me the operation to initiate the new drive failed.

After dropping it off at UPS for a return, suddenly this error message starts to pop up. The size meta suggests this is for another WD drive that has not been disconnected from this Mac for at least 3 years. And I clicked on Eject, it does not work. Of course I could not mount or initialize since the physical drive is not even with the mac.

Disk Utility, with its integral First Aid feature, is one of very few utilities that has survived relatively unchanged since the first public beta-release of OS X. One significant change has been the merging of verify and repair into the single First Aid button. This article looks at two contentious issues in First Aid: whether you need to run it on APFS volumes and containers, and how to work round the status 65 bug that can prevent First Aid from working.

Select an APFS volume and click First Aid and Disk Utility runs a command like
fsck_apfs -y -x /dev/rdisk5s1
on that selected volume alone. The -y option tells fsck_apfs to repair any errors that it can, if it detects any, and the undocumented -x option runs this through its XPC interface to the Disk Utility app. Note that the volume is specified using its raw device name of rdisk5s1, and not the block device disk5s1. As mentioned below, this overcomes any inconsistencies that could arise with caches.

When you want to check and repair a specific volume, the best option is to select that volume and run First Aid on it. If that returns any warnings or errors, then follow that by running First Aid on its container too.

When you want to check the health of all the volumes in a container, the best option is to select that container and run First Aid on it. As that checks and repairs all volumes in that container, there seems no point in checking them individually unless you suspect them of having problems, in which case you should do that before checking the whole container.

APFS keeps a count of all volumes mounted within each container, nx_num_vols_mounted, which is incremented each time a volume is mounted, and decremented each time a volume is unmounted. APFS will only unload a container when nx_num_vols_mounted is zero, i.e. all its volumes have been unmounted.

I have previously described how you can manually unmount Time Machine backup snapshots; a far simpler method in Disk Utility is simply to select the disk and unmount that, which now appears reliable. Once the disk has unmounted, select the volume or container you wish to check and repair, then click on First Aid.

Talking about disk utility , i never been able to show apfs snapshot of the timemachine volume (just 1 month of backups, around 57 snapshot including 24 local for a grand total of 300 GB , 2 GB on disk ) , it just run for more than 5 minute but nothing is shown. Tried with different mac , with monterey and ventura, same result.

Oh no , it is just a dummy volume to reserve hdd space (and avoit the TM volume to grow up without notice it) , i like to be informed when the TM volume will reach 500 GB size , in that case I will delete the dummy volume and create another one of 400 GB and so on. This is the only solution until Apple implement reservation without destroy and recreate the volume

Done in recovery mode , no issue found , it check all the 56 snap. Removed the disk , start with a fresh disk a new Time Machine backup , at moment there is only 1 snap on the disk (first backup) + 22 local snap. It still not able to show the snap on the TM disk (it show correctly all the local snap on macintosh hd)

OK, I assumed that generally partitions would be inside containers of the same number. It made me pause for thought as it seemed odd that you had /dev/disk4s2 inside /dev/disk5 and I wondered if there was a significance to the example.

As I laid out for the sake of this example, disk4 is partitioned into disk4s1 and disk4s2. The latter is also the container disk5. In APFS, partitions and containers are the same thing, but have dual names.
Howard

This CD is pretty special. It contains printer drivers for both Windows andMac, and is split in two parts. Mac OS only mounted the Mac-readable part,which is on device /dev/disk4s1s2. As you can see, this part is only 50MiB, which is less than the 266 MiB that we're expecting. If you check whichdevices actually exist in /dev/, you'll find

4.Look for the volume with FileVault set to Yes that you want to decrypt, select it's identifier, such as "disk4s1" and cmd-c to copy. Note that there may be more than one volume with FileVault enabled, if so, look for the "- Data" volume.

8.Type the below command and paste in the volume identifier you still have in the clipboard. Next, look for the UUID for the Local Open Directory User entry from the command above, select and copy it, then paste it to the end of the command, and run it to start the decryption process.

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