Thanks for this example.
I had used:

iris session ${INST} -U %sys << EOF

w "stopping the mirror 1 is sucess: " zw ##class(SYS.Mirror).StopMirror("PMIR") h
EOF

The only way to get an estimate I can think of is running the compact against a SAN snapshot on similar hardware.
The free blocks could be anywhere in the file and that plays a big role.

Here are some numbers:
Current Size: 2332950 MB
Freespace at end of file: 300 MB
Total freespace: 8957 MB
Blocks Scanned: 10850564
It took 1 hour 44 minutes

The truncation was almost instant.

There appears to be this Using Log Monitor.

I use external tools to examine logs like cconsole.log though.

Was so happy to discover d ConvertShadowDatabases^MIRROR

First my experience is on IRIS.DATs that were 2Tb is size and experience will vary widely since where the free space is is what matters.

There are two different compacts:
Compact globals in a database
Compact free space in a database
If all you want to do is compact free space things are easier.
Do it in small steps with ^DATABASE
Current Size: 2307950 MB
Total freespace: 8564 MB
Freespace at end of file: 18 MB

Target freespace at end of file, in MB (18-8564):200

One great feature is you can cancel if you need to.
Press 'Q' to return, 'P' to pause, 'C' to cancel:

Truncation can be done in the same way in steps.

If you have one I suggest that you do this on your DR instance, move to DR and then do it on what was production.

If you are using 8k blocks for IRIS you should start thinking about the 32Tb limit for 8k databases.
You need to run an integrity check after you are done.

If you wanted to run compact globals that is much more complex.

If the underlying storage does deduplication you should make sure you have extra space at that layer.

AIX 7.3 TL1 defaults to OpenSSL 3.x
$oslevel -s ; openssl version ; uptime
7300-01-02-2320
OpenSSL 3.0.8 7 Feb 2023 (Library: OpenSSL 3.0.8 7 Feb 2023)
  08:58AM   up 72 days,  11:32,  16 users,  load average: 7.04, 8.57, 9.52

You can compact the globals inside the IRIS.DAT files.

You can purge journal files automatically.

These are all short term measures unless something is wrong and you can fix the root cause.

From Replacements for ObjectScript $ZUTIL Functions

Locks are part of gmheap but you could allocate them in advance locksiz.
Can you run irisstat?

Did you try IRIShung?

locksiz is in bytes, uses a subset of gmheap memory and is dynamic. Here it the older Cache version.

gmheap is in megabytes and is static. The default in IRIS is 0.75% of total RAM. Here is the older Cache version.

You can monitor memory usage in the System Management Portal.

Can you give an example?

Do you mean something like this?

iris session ${INST} -U %sys << EOF
w "stopping the mirror 1 is sucess: " zw ##class(SYS.Mirror).StopMirror("MIRROR") h
EOF

If you don't know Mac/Linux you would have to deal with learning both.
If you are doing code development connecting from a Windows workstation it might be easier to connect to a locally installed instance and takes less hardware.

Have you tried using the console version of task manager?

I would do that first.

If you have another Ensemble instance you could figure out where the in the system tasks are stored using journalling and making a change to a task.

Once you know where the task is stored to just kill or change the associated global.

You wouldn't import it like a SQL dump. It is the IRIS native database file.

You could just mount it and then use it directly.
Look at this documentation.

There are several major steps:
Mount the LUN or LUNs as a filesystem
Have the required namespace
Mount the CACHE.DAT in Cache. Look at ^DATABASE
Have the required global mappings.

My suggestion is to install another instance of Cache on the server.
That way you might be able to update the cache.cpf using the one from the old server as a template.

This is a pretty complex task.

AIX 7.3 TL 1 and later has OpenSSL 3.X

From the linked IBM page AIX 7.3 TL1 was released six months ago.
$oslevel -s
7300-01-02-2320
$openssl version
OpenSSL 3.0.8 7 Feb 2023 (Library: OpenSSL 3.0.8 7 Feb 2023)

Easiest way would be look in the cconsole.log in the instance directory.

ccontrol qlist has information about the current mirror state on that server but you need a before and after to know if there was a failover.

Are you sure this is not a umask issue?

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/…

This documentation page explains how to add a gateway.

Not sure how critical the notifications are in your use case but there have been some massive SMS gateways outages.

An on premise SMS device would also send messages when the connection to the internet down.

There are OS tools that allow you disconnect from a running session like screen.

As a guess you have more mirrored datasets then expected. I have seen User get mirrored for example.
What does this show on the primary?
d ^MIRROR -> 1) Mirror Status -> 1) List mirrored databases
 

If both TESTTC01 and TESTTC02 existed before starting, your refresh process is also overly complicated.
You should be able to shutdown TESTTC01 & TESTTC02, copy the file from TESTTC01 to TESTTC02, start TESTTC02 and do a Activating and Catching Up Mirrored Databases. If you have a backup or snap of the file you don't even need to shutdown TESTTC01.

There are five expansions in less than a single second. Maybe you ran into a race condition.

d ^MIRROR on the primary shows the data of the target mirrors so the data is available.

The documentation topic is here.

%SYSTEM.Mirror can give you information but only about the instance you run it on.

w $SYSTEM.Mirror.GetMemberStatus()
        Primary