Can I add external HD to time capsule for additional mac?

I thought i just told you how.

(And that it was not necessary as the internal disk will be fine).

So please do it.. exactly as I explained.

1. Plug the USB drive into the TC.

2. Open your airport utility on the Mac.. and check that the USB drive shows on the drive tab.

Here is my 3TB TC and I plugged in a 320GB drive which is HFS+ formatted. ie Mac OS extended journaled.

If it does not show up, you did not buy a Mac compatible one.. which means it is formatted PC. (NTFS) which will not work.

If you need to reformat it plug the USB drive into your Mac and open disk utility and reformat the drive Mac OS extended Journaled.

If you need instructions for that please ask.. but there are lots of websites a simple google will get you to.

3. Once you have it showing as available disk in Airport Utility open Time Machine.

Click on select disk.

Click on your USB drive.

HOWEVER there is no need to do this.

Look at the free space on your TC. Both the airport utility disk tab and TM preferences shows you the free space on the drive. I have been backing up a few computers for ages but they have only small amount of data on them so you can see it has 2.3TB free space..

As long as your 2TB drive has plenty of free space .. say 1TB then you can easily manage backups to the same disk without it getting mixed up.

Let me show you mine.. I have 5 separate backups on it.. each is called sparsebundle disk image with the computer or other name I have given it.

My TC is about 6 years old

Your TC is the latest.. and is at most just over 3.5 years..

I took you too literally so my comment about the TC power supply is also wrong.. the Gen5 TC has more than enough power to handle the USB drive.. but it is even less reliable using USB drives than it was on the earlier one.. so I would definitely NOT recommend you use USB on it.

As with everything YMMV.. and there is no one right answer. But I have tested USB on lots of models of the TC and found I have issues with them disappearing from the network, never spinning down and general unreliable access. Plus it is just plain slow. Using the internal disk is far superior way to use TC.

Certainly if you have a Gen3 TC.. look on the base .. if it is A1355 then it is getting a bit old.. the A1409 could last a bit longer.. you can always remove the hard disk to get the current backups

Again my comment was directly related to your 6 year old TC.. which we now know is much less.

The ifixit site is correct if only barely sufficient info on replacing the hard disk. It is not easy on the latest model which you have.. early ones are much easier.. You need a special long reach T8 screw driver. And the cable on the hard disk is extremely delicate and no replacements are available. People up end the TC and the disk slides down and rips the cable. So be very very careful. The hard disk has special rubber mounts specific to that model drive.. and it fits no other model. Overall I do not think replacing the drive is a good idea.

But you can always pull the drive and use a USB enclosure and plug it into the computer directly to recover the backup. It doesn't matter if you damage a dead TC. you are removing the hard disk not replacing it. Since the drive is probably not the part that will fail in your TC.. rather it will die of overheat or fan issues or power supply problems replacing the hard disk is pointless.. but you can indeed recover your files easily enough.

Open the TC disk in Finder and check the size of the sparsebundles. If the one for your old MBP is really huge it is probably time to make a decision if you want to delete it and even now is the time to archive the TC and start over.

Time Machine will keep expanding until it fills all available space .. that is correct and what it was designed to do.. but eventually you reach a point where you do need to make a decision to either save all the backups and then restart or just restart.

I would still use the TC properly and its internal disk will give alot less trouble than a USB plugged into it. Small self powered drives can easily kill an old TC power supply.

So your options are to archive the TC to the 2TB disk you just bought.. Archive button is on the first screenshot I posted on the disk tab of the TC in airport. It will take a long time so I would start it going to bed and leave it to run for 12-18hours .. you will not be able to backup during that time. Once you have an archive.. use the erase button also in the same area.. and you can just do a quick erase ..

Then you will have a clean TC to start over.. begin the backup of all the computers.. not at once.. but one by one.. using ethernet if possible.. buy a thunderbolt to ethernet dongle if you need to.. they are cheap and the best gadget going. That will drop the time to do the initial backup to just a few hours even with a full 256GB disk.

You can also do it by wireless but make it as fast as possible by parking the laptop right next to the TC.

Once you have got 6 months of backups from your computers their is very little need for the old archives. You can then wipe the disk and use it for a secondary backup or whatever you want. Particularly if the TC does become unreliable another archive could be of value.

That is how I would proceed.

There are other alternatives.. up to you..

Certainly if you have a Gen3 TC.. look on the base .. if it is A1355 then it is getting a bit old.. the A1409 could last a bit longer.. you can always remove the hard disk to get the current backups if you have issues.. that is relatively simple to do.

One of the other folk here might post with other ideas. Here is standard answer from Bob.

My Time Capsule has too little space for normal backup. How do I erase older backups to free up space?

is it possible to do that? For example, can I connect the Seagate HD directly to the time capsule via USB, then use it for backing up the MBP (while continuing to use the time capsule for backing up the old MBA)?

Sure that is fine.

Plug it into the TC and it will show up as an available disk.

Open TM preferences and choose the USB drive as the backup location.

Then do the backup.

could anyone suggest me a best solution to my problem

Just to check that you don't think this is necessary.

You can backup multiple Macs to the internal disk of the TC.

TM backs up each Mac to its own special disk image called a sparsebundle.

Absolutely no need to plug in extra disk unless you have a space issue and I doubt it on a 2TB TC unless you are using it to store files.