Any book or website that explains macOS / iOS for technicians?

I am a learning technician and I would like to know a book or website that explains certain aspects of macOS and iOS that are not found in the best known books (such as macOS Support Essentials, which I already have).

For example: I am learning how the Photos app organizes photos internally on Apple devices (such as how photo editing is stored, sidecar files, how to restore a damaged photo library, etc.). Is there a website or book related to these everyday things for technicians?

I know my question is a little complicated, but I'm a little tired of having to read article after article and forums to learn this.

Any help very welcome.

Hard drive: what explains the intermittent I / O errors for all attached volumes?

Two external volumes that have I / O errors. This is a small part of the console output. One is an SSD and the other is a normal hard drive. Both are relatively new.

default 18: 46: 56.035095 -0800 kernel disk2s2: I / O error
default 18: 46: 56.084555 -0800 kernel disk3s2: I / O error
default 18: 46: 56.133860 -0800 kernel disk2s2: I / O error
default 18: 46: 56.182963 -0800 kernel disk2s2: I / O error
default 18: 46: 56.232262 -0800 kernel disk3s2: I / O error
default 18: 46: 56.288224 -0800 kernel disk2s2: I / O error

What would explain the I / O errors for two different volumes?

Both are connected directly through a USB-C hub. The same problem occurs when they are connected separately through a USB-C to A cable to my MacBook Pro.

All the diagnostic tools I have tested say that the units are fine. This includes Techtool Pro, Drive Genius and DiskWarrior. The console does not show I / O errors while these tools perform a surface exploration or reconstruction.

When mounted for the first time, both units appear normal, but after 30 to 40 minutes, both remain mounted but all the files are missing in the Finder window. duh from a terminal it shows that all top-level folders are empty but there are no sub-folders. After reassembling each unit, all files are intact.

Is there any way to rule out / hardware problems and if so, how? Could it be an HFS / AFPS problem? Both units are HFS but the start volume is AFPS. At this point I do not believe that they are the units themselves.

mysql: explains in view the derived programs while explaining in select sample type of simple selection

I have a view v which implies a couple of sub-selections in your SELECT clause plus a couple of meetings by I.D or indexed column.

The view query is like:

SELECT col1, col2, (SELECT ... FROM subt) AS COL3 FROM t1 JOIN t2 IGNITION [..]

The fact is that if you consult that view col1, which is pk of t1:

SELECT * FROM v WHERE col1 = & # 39; some value & # 39;

the EXPLAIN shows a lot of DERIVATIVE tables, but if I execute the same query in the view SELECT declaration:

SELECT col1, col2, (SELECT ... FROM subt) AS COL3 FROM t1 JOIN t2 IGNITION [..] WHERE col1 = & # 39; some value & # 39;

those same tables appear as SIMPLE.

How is that? I need to correct that view because it is not using some indexes (although all the links are by pk or indexed columns), but I'm stuck in those DERIVATIVE Rows and I can not go further in my analysis.