Time Machine-Silion Mac-Apple Airport Extreme - USB Disk Not Found

Two possible explanations.

Some mentioned that only the Airport Extreme 802.11AC supported external USB hard drives. Is that a correct statement?

Yes. For AirPort Extreme Base Stations Time Machine is only guaranteed to work with the latest production 802.11ac AirPort Extreme Base Stations — the "tall" variety. Refer to Backup disks you can use with Time Machine - Apple Support which makes the distinction abundantly clear.

There is extensive history on that matter, which began with Steve Jobs mentioning in an offhanded comment that TM could be used with any AEBS. It just wasn't so. Apple's Support documents never indicated it would. There was probably a lot of internal turmoil going on that we will never know about. No one wanted to say "you're wrong Steve" even though he was. In any event the introduction of the new "tall" AEBS models put the matter to rest. It was Apple's first officially documented and unequivocally supported non-Time Capsule NAS backup solution.

The 802.11n "flat" base stations may work with Time Machine. Lots of people reported that it did, but it was never officially supported.

It goes without saying all Time Capsule models work, all the way back to and including the original one. They work to this day. I still use them.

Next:

Is it the choice of how the security of the shared disk is selected?

Possibly. If you encrypted that backup disk separately, don't. It won't work. Erase it using the GUID Partition Map and Mac OS Extended (Journaled) because that's what the AEBS will be able to read. Then, when adding it to TM check the box to encrypt backups. That way, the backups themselves will be encrypted, as they should. Don't encrypt the entire disk. That's only useful if the drive is directly connected to the Mac.

Time Machine in Sonoma requires an APFS formatted drive, which negates your using the AEBS with the attached drive. Just mount the APFS formatted drive on your MacBook Air with a USB-C cable, tell Time Machine to use it, and the rest will work fine.

I use an APFS formatted Crucial X9 2 TB drive connected to my M1 MacBook Pro M1 Pro for use with Time Machine. The drive fits in the palm of my hand with room to spare so not a portability issue.

No need to apologize; it's a common misconception that "discontinued" = "unsupported". The latest macOS Time Machine instructions include the latest TC models — as well as the recent AEBS, which as I wrote is a first for Apple's Support documents.

Apple also updated the firmware for those devices long after they discontinued them.

Years ago I did purchase a Synology NAS device. It was never reliable with Time Machine. After several weeks of testing, reconfiguring and simplifying my network to their liking to the point it could not be made any simpler, updating software, backing up / restoring (or trying to) and generally beating my head against a wall I gave up on it, returned it to them and they very reluctantly refunded my money. Since then I have relied exclusively on genuine Apple AEBSs, Time Capsules, inexpensive USB hard disks connected to them, or directly connected to the Macs they back up. They have been 100% reliable. Not 99.999% but 100%. Not one failure to back up or restore, ever.

I understand some people successfully use the Synology with Time Machine but that was not my experience, and not one I am likely to ever repeat. Weeks of wasted time.

As far as Wi-Fi speeds the 802.11ac base stations Wi-Fi speeds exceed Gigabit Ethernet. Not that it matters to TM because backups are a low priority task that comes nowhere near the throughput 802.11ac base stations are capable of.

The original "flat" Time Capsules use external power supplies and maybe that's a better idea, but I haven't had any power supplies fail either. Nothing lasts forever though, but I miss the fact they just worked without difficulty or complaint.

External hard drives seemed like a better option with an Airport Extreme.

They are, since they're cheap and disposable, but I have never attempted to use Time Machine with an 802.11n only Extreme — the ones no longer supported. With the understanding that everyone's backup requirements are different, backups are too important to me to risk unsupported configurations. Even if it "worked" I wouldn't advise anyone else to do it. That's also why I gave up on Synology. They lost my trust. Not that they earned it to begin with... their tech support never seemed very competent to me, and were quick to blame anyone and everyone but themselves for their failures.

Judging from other reports on this site I put the Western Digital "MyCloud" in the same category. Never tried Ubiquiti. Maybe one day.

Bottom line, to get an Airport Extreme to work with Time Machine, I am going to have to get a used 802.11AC

Or a used Time Capsule. Any model will do all the way back to the original one, although later models had larger capacity drives and are more desirable. They used to be inexpensive on the used market but their prices have been creeping up. If you can find one at a reasonable price, I'd get it.

VikingOSX wrote:

Time Machine in Sonoma requires an APFS formatted drive, which negates your using the AEBS with the attached drive.

Not exactly. Although I agree using an 802.11n-only AEBS is not supposed to work for reasons I explained, APFS is not the reason.

I am using Time Machine for backups hosted on Time Capsules as well as the latest production 802.11ac AEBS with HFS+ formatted drives connected to their USB ports. Obviously those devices cannot read APFS. It makes no difference to TM for the simple reason they are NAS devices. The file system is not a factor. A Synology or Ubiquity NAS device as OP proposed would be out of the question if it were.

I wonder if the case-sensitive has something to do with it.

• If any source volume is case-sensitive, then its TM backup disk is required to be case-sensitive.
• If no source volume is case-sensitive, then the backup's case sensitivity is optional.

See if you can use Drive DX to possibly get a better view of Drive health…

https://binaryfruit.com/drivedx

It's not entirely clear to me what you're trying to accomplish. If you need reliable Time Machine backups you will not accomplish that goal using unsupported equipment. On the other hand if you simply want to experiment that's ok.

Even the 802.11AC (tall one) is unsupported by Apple now ...

???

Wherever you're getting your information, it's wrong. It and Apple's other 802.11ac devices remain fully supported, just as much as your MacBook Air, despite the fact they have both been discontinued.

It seems that you have not read the Apple Support document I provided. Time Machine will work... if you let it. Just follow instructions.

The is likely to be the case for your Time Capsules. Perhaps their fans were merely clogged with dust, and perhaps that led to premature hard disk drive failure. Fans can be cleaned and drives can can be replaced. Maybe Apple should have used bigger, noisier fans? Who knows.

Yes it would be nice if Apple started production on new wireless NAS devices, but who knows if or when that will ever happen. Their decision to discontinue their entire AirPort line of products was one of their more boneheaded moves in my opinion. It seems if Apple can't sell a few hundred million of something they're not interested.

you want to avoid case sensitive and let your internal drive is case sent to you, which is not recommended.