Changes to SD card do not persist after unmounting

I have a couple of 128GB Samsung EVO+ micro SD cards. I have two different means of connecting these to my mid-2012 MacBook Pro running MacOS 10.13 High Sierra: a micro-to-fullsize SD adaptor, which I insert into the MBP’s card reader slot, and a Lexar microSD-to-USB adaptor, which I insert into a USB slot.

I can read from both cards without issue (save that the OS only seems to notice a card in the card reader slot about a quarter of the time). The exfat volumes on the cards mount and files on them can be accessed. Disk Utility shows “Writable: Yes” in the Info window for the mounted volume. mount shows that the volume is mounted properly, with no read-only flag indicated.

Yet, if I make changes to the volume, for example by entering

cd /Volumes/S7; mkdir tmp; echo 'testing' >> tmp/test; 

these changes appear to have been made successfully, but upon remounting the volume, neither the file nor the directory it was created in are anywhere to be found.

I have similar problems when using fdisk to change the partition type (my actual goal right now) so I can use the SD card (and its contents) in my Android phone: changes to the MBR partition table appear to be written successfully, but then are not apparent when the partition table is displayed immediately afterwards.

Other USB volumes (for example, an external hard drive) work correctly. I haven’t tried using any other SD cards yet.

These problems occur with both SD cards, whether connected via the fullsize adaptor or the USB adaptor.

I upgraded from 10.10 relatively recently and suspect that these problems have started since the upgrade. Are there any similar known issues with using SD cards under High Sierra or other MacOS versions?

macOS Mojave – Time Machine – not unmounting network drive

Got a problem with Time Machine that appears to be Spotlight related.

Time Machine is not unmounting/ejecting the network backup drive which is preventing me from do stuff on the backup drive.

Time Machine log:

[com.apple.TimeMachine:TMLogInfo] Ejected disk3 from '/Volumes/com.apple.TimeMachine.TM_Prime-DA16D91F-3320-4834-91ED-2902CE57E46D/Graham's_Mac.sparsebundle' [com.apple.TimeMachine:TMLogInfo] Failed to unmount '/Volumes/com.apple.TimeMachine.TM_Prime-DA16D91F-3320-4834-91ED-2902CE57E46D', error: 16 Resource busy [com.apple.TimeMachine:TMLogError] Failed to remove directory '/Volumes/com.apple.TimeMachine.TM_Prime-DA16D91F-3320-4834-91ED-2902CE57E46D', error: 16 Resource busy 

It’s a metadata thing:

Grahams-Mac:Volumes Graham$   sudo lsof /Volumes/com.apple.TimeMachine.TM_Prime-DA16D91F-3320-4834-91ED-2902CE57E46D COMMAND PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME mds      82 root   15r   DIR  52,32      264    2 /Volumes/com.apple.TimeMachine.TM_Prime-DA16D91F-3320-4834-91ED-2902CE57E46D 

Disabled Spotlight for a range of drives. Time Machine uses a different name each time.

Grahams-Mac:Volumes Graham$   sudo mdutil -i off /Volumes/com.apple.TimeMachine.TM_Prime* /Volumes/com.apple.TimeMachine.TM_Prime-DA16D91F-3320-4834-91ED-2902CE57E46D: 2019-04-27 18:22:26.919 mdutil[2929:1075028] mdutil disabling Spotlight: /Volumes/com.apple.TimeMachine.TM_Prime-DA16D91F-3320-4834-91ED-2902CE57E46D -> kMDConfigSearchLevelFSSearchOnly     Indexing and searching disabled. 

Unmounted the drive

Grahams-Mac:Volumes Graham$   diskutil umount force /Volumes/com.apple.TimeMachine.TM_Prime-DA16D91F-3320-4834-91ED-2902CE57E46D Unmount successful for /Volumes/com.apple.TimeMachine.TM_Prime-DA16D91F-3320-4834-91ED-2902CE57E46D 

Run a Time Machine backup. Same issue.

Any help would be appreciated.

External media unmounting after a certain length of time on Kubuntu

I have set up a server that hosts all my files which is connected to 4 4TB HDD’s in an external enclosure which is located next to the machine running the server. But, after a while, the external disks are no longer mounted and the drives show up in Dolphin as having broken links (little orange icons with broken links on them). The only way to return them to working order is to reset the system and reboot Kubuntu. As you can imagine, this isn’t ideal, as the only reason I set up the server is to have somewhere that I can access my files at any time, something I can’t do if my drives are randomly unmounting themselves. Turning the enclosure off and on again does not help, neither does changing the USB port that it is connected to. How do I fix this?