Time Machine disk replacement

I see lots of discusssion on this topic but mostly going back three or four years.

My Time Machine backup drive for my 2023 Mactook Pro is full.

I have used a Western Digital Blue 2T SATA drive for time machine for the past six years. It has worked flawlessly but is now full. I do not want to start a new backup on this drive and lose my incremental backups. So I am looking for a new drive. I also use backblaze for off-site backups.

Is it worth the cost to go with ssd? I need at least 4T, high reliability, and usb-c connectivity. If not SSD I can get a WD blue or black 4T non-ssd drive. WD Passport has lots of recommenations but judging from the comments it suffers from disk failure and is not under consideration.

What suggestions do you have? Are there reliability statistics for what you recommend?

If the TM drive is always attached then going SSD probably isn’t worth the cost except for the “they’re really small if you get a Samsung T7 Shield or equivalent” route IMO. If you’ve got a desktop Mac that’s always on…lol ing your own TM via wifi using CCC is proven to work far better than TM over the network…ask if you want details on the best way to set this up, and a spinning drive is just fine on this case plus you can schedule it for say every 6 hours or daily of that suits needs better.

Relying on Josh Centers’ buying advice last year I got a couple of 1TB Toshiba Canvios for TM backups and they work fine, never a problem with either, and the price is fine, much cheaper than SSDs. I’m satisfied and can recommend it. Of course, the speed’s much (very much) slower than an SSD (which I also have), but speed’s not that important for TM. It comes only with USB-3.2, but I plug that into a USB-C adapter and use them on both M2 MBAirs.

For Time Machine? No, I don’t think so. You don’t need high performance. You need lots of capacity.

I would suggest getting a very large 3.5" 7200 RPM HDD that is rated for 24x7 operation. For instance, Micro Center is currently listing a 10TB Toshiba N300 for $190.

Install it in a USB3 enclosure that has a fan (because high performance drives can overheat without active cooling). For instance, Micro Center is currently listing a Vantec NexStar HX-35 for $35.

When shopping, be sure the enclosure supports the size drive you plan to buy. The Vantec enclosure I cited claims support for 16TB drives. The other “with fan” enclosure sold by Micro Center says it only supports drives up to 4TB. I don’t know if a larger drive won’t work, or if they simply don’t support it, but it’s something to keep in mind when making a purchase decision.

Anyway, once you select a drive and enclosure, it is very easy to assemble the two pieces together into an external drive. It will almost certainly outperform a retail external HDD and might also cost a little less.

That having been said, getting a big drive is only the first step. What do you want to do with your old backups?

If you’re just going to disconnect and file the old drive, then you’re good to go. Just connect the new drive, format it, set up Time Machine, and you’re done.

But if you want to clone your existing backup drive to the new drive, that could be a challenge. You can’t use a normal file-based backup utility to clone a TM volume, because it is going to contain dozens (or hundreds) of snapshots - one for each backup. A file-based clone process will only be able to copy one.

I haven’t tried this, so I don’t know if it will actually work, but I think you should be able to use software capable of making a block-level clone (that is, copy all the logical disk blocks, without regard to the file system). Once that’s done, your new drive should be a clone of the old drive - with the old drive’s capacity. But once that’s done, you can use Disk Utility to resize the APFS container holding the TM volume(s), allowing it to use the full capacity of the new drive.

Some tools worth considering for this task:

  • The command-line dd tool. Fast and flexible. No UI at all. No safety net - you can completely trash everything if you get the parameters wrong.

  • The “Restore” option in Disk Utility. Select the new/blank drive. Then click “Restore”. Then select your TM volume as the source.

  • Balena Etcher. I’ve used the Windows version of this to make bootable SD cards from image files for use with my Raspberry Pi.

See also:

1 Like

FWIW, BackBlaze releases an annual report of the relevant performance and reliability of most makes and models of drives available for consumer backup.

You don’t get an SSD for the performance. Modern TM to APFS is i/o throttled anyway by macOS. And it is true, that per GB even the cheapest SSD is still more expensive than spinning rust.

You do get an SSD though because you don’t want to have to get a large external case with a power supply and a fan that makes noise right next to where you work. And because you don’t want to have to cope with mechanical storage making noise and dying its inevitable mechanical death before you’d like it to.

There are people with extreme capacity requirements who have no choice but to go HDD. But most of us have more modest requirements. Add to that I’d argue rather than get the biggest drive for TM so that you can use it for the longest, it makes more sense to get something with moderate capacity that you replace sooner (relatively speaking, it’s still many years not months we’re talking about). That way you’re always buying from the least expensive GB/$ range of the market and you’re not relying on an increasingly old drive (not to mention interfaces change too). You can always hook up that old TM disk if indeed what you’re looking for isn’t on the currently hooked up TM drive.

Here’s a decent quality 4TB SSD for $145. It’s fast, small, silent, and it will last for many years. It comes with a SATA interface which is fine because TM will never get close to maxing out the ~600 MB/s bus limit. And since this small disk has a SATA interface, it can be connected to your Mac with a bus-powered very small, silent, and cheap USB enclosure such as this one for $23.


Whatever you do, don’t buy preassembled kits like Samsung T7 or similar. I know their names get tossed around a lot because of course that’s what places like Target stock so that’s what people get when they buy off the shelf. But it’s a waste of money and these drives often have an at best average reputation (at least with Macs, i.e. APFS). Even if you end up going HDD, buy disk and enclosure separately, assemble yourself. Requires 2 min and a screwdriver (for SSDs usually not even a screwdriver). Anybody can do it. Use $ saved to get SSD over HDD. :wink:


Personally, I do not think an SSD is a good storage medium for Time Machine because like @Simon said, TM is throttled and does not take advantage of the write speed of the SSD. However, SSD goes really well with Carbon Copy Cloner - my typically backup operation takes 3-5 minutes. This is really advantageous when I need to leave my desk frequently throughout the day, for days at a time.

I find many general points made in this discussion thread about SSDs and HDDs informative and helpful:


Reluctant as I am to contradict you, Simon (because you undoubtedly know more about such things than I), I believe you’re not altogether correct. At about 8x10x1.5 cm, my Toshiba Canvio is only a little bigger (but flatter) than a pack of cigarettes (yes, my SSD’s about half that, but is that really significant?), is hardly audible and needs no additional power source, fan or other cooling. Agreed, lifespan’s 2 to 3 times longer with SSDs, but doesn’t the price difference still argue that the HDD’s a better buy in the long run?

Thanks all. Good comments from everyone and nice suggestions. After much thought

  1. no to ssd.
  2. get a new (and bigger) wd sata drive in blue or black.

Should easily last me another six years, takes up exact amount fo disk space, already has the usb to usb-c connector. The price is right, the disk is quiet, and it should work.



While you can keep years and years of backups on a Time Machine disk, you should really think about whether it’s the right thing to do.

Backups are primarily designed for recovery of a system from a data loss event (disk crash, “oops”, file deletion). If you have to recover from something more than a few weeks old, you may have more problems than just restoring from a backup.

Most people don’t need to keep most of the data that’s backed up with Time Machine for a long time.There’s usually only a subset of files that are really important and need to be archived for long-term storage. If you have files that need to be kept for over 6 months or so, you might want to rethink how you’re storing those items for long-term retention so that they’re better protected and “future proofed”.

Just remember, one burp on your Time Machine drive and years of work may be irretrievably gone.


I think that’s indeed a valid point.

I do assume, however, when we are talking HDD over SSD for cost reasons, that we are talking 3.5” SATA HDDs which are big, need power, sometimes noisy, and often come with fans. You are right that a 2.5” SATA HDD doesn’t come with those deficiencies, but then you’re also giving up a significant part of the $/GB advantage over SSDs.

My experience with drives that you buy as externals is that they may be housed in the cheapest enclosures the vendors can get away with. I’ve pried open at least 4 Seagate externals after they “failed”, after testing to make sure the problem wasn’t the cable. The drives themselves were all fine, as I suspected they would be. I only had those Seagate externals because we got them for nothing.

I’ve been using OWC enclosures for 3.5" and 2.5" drives for many years. They are reliable and hardly noisy enough to disturb anyone, unless they have ears like a bat and need absolute silence in their workspace.

I can’t see wasting a SSD just for Time Machine. Just get a decent enclosure and a 6TB or larger Toshba 3.5" drive.


Speaking of OWC enclosures…does anybody have an OWC ThunderBay (4 drive model) and a decibel app on their iPhone…if so can you give me the noise level of the RAID? I’m wondering how much louder the 3.5 strive one is than the ThunderBay mini 2.5 drive version in case I ever need more than 12TB. Using an app named Decibel Meter on my XS Max it shows 38dB right at the front of the enclosure and 36 1i inches or so away at my normal ear location while editing photos on the Studio.

Far be it from me to tell someone that their preferred device isn’t a good choice, but my experience has been that most of those pocket/portable HDDs are very low-performance devices. They’re typically 5400 RPM or slower and may also use SMR recording.

It may be OK for Time Machine, but I’ve always preferred the performance of a 7200 RPM drive.

Of course, you may find that portability and convenience are more important.

When picking your drive, look up the specs. Get a drive that uses CMR recording and is rated for 24x7 operation (which is the use-case for Time Machine).

You may have a hard time getting this information for a pre-built USB drive, but you can usually get this information for a 3.5" drive (which you’ll then put in your own enclosure.)

For WDC’s drives, I would look at the Red Plus, Red Pro, Gold or UltraStar models. I would avoid the Red (non-Plus/non-Pro) - it’s an SMR drive. And I’d avoid the Blue or Black models - they are not rated for 24x7 operation.

1 Like

You’re right in the details, but: I make once-daily TM backups. I don’t need to recover stuff from a TM very often (rarely, in fact, but when I need to it’s important). Speed isn’t terribly important, nor portability. What was important was price and plug-n’-play simplicity (and, as I mentioned, Josh Centers’ buying advice), the small footprint is a plus, and that’s what I’ve got: it does what I want when I want it.

That changes everything.

On my Mac mini, my TM volume is connected and the system is powered-on 24x7. So it’s making hourly snapshots every hour, every day.

But if your Mac is not powered all day, or if you only connect the drive once per day, then you clearly don’t have a need for a fast or a 24x7-rated drive.

And you may not require an enclosure with a fan, since your backup will probably complete before the drive gets hot enough to overheat. (FWIW, I don’t have fans on the two external drives I use for making clones. They’re only powered on once a week or so for a couple of hours as I make a backup, then they’re unmounted and powered-off until next time.)

But one could also argue that you don’t need TM for that kind of operation. A clone utility that makes snapshots on an APFS destination (like CCC) may work just as well.

Just so I understand, since TM is making snapshots only a fraction of the time, does the drive itself work 24/7?

Thank you,


Depends if you’ve set up the HDD to sleep itself during inactivity and if the drive/case you have support properly doing that.

Of course if TM backups get more substantial, time to completion becomes longer (compared to the 1-hr interval between snapshots) and at some point the duty cycle is no longer low – you’re drive will be spun up most of the time. If OTOH your snapshots are very small, TM backup is short (say on the 1-min scale), and your drive indeed spins down in between, you’ll be fine.

It’s not (normally) making backups 24x7, but the drive is powered 24x7. TM makes a backup/snapshot every hour. Depending on how much data changed in the past hour, that might take a short time (1-2 minutes) or it might take a long time (30 minutes or more).

This is in addition to any other access macOS may be performing as a part of its various background/housekeeping tasks. I know Spotlight doesn’t index TM volumes, but I frequently notice activity between backups, so there is some kind of housekeeping taking place.

Consumer drives (those not rated for 24x7 operation) are designed with an expectation that they will be powered off (or put to sleep) most than 50% of the time. Some people call this “8x5” operation - in use during business hours only. The expectation is that when you’re not actively using the computer, the drive will be powered off or asleep, which is going to be most of the time.

If you are a person who powers off (or puts to sleep) the computer when you’re not using it, then an 8x5 drive might be just fine. But my desktop systems act as household servers, so they never shut down and never sleep. (My laptops are put to sleep when not in use, but they never hold any data I can’t afford to lose, so I don’t back them up.)

All this having been said, I’ve used consumer drives in always-on system configurations and for the most part, they’ve worked just fine. And Backblaze’s statistics support this (they’ve found that consumer drives are just as reliable as enterprise/server drives), but I believe (maybe incorrectly) that if the manufacturer advertises it for 24x7 operation, it will be more reliable than a drive from the same manufacturer that doesn’t advertise this.

After switching from a spinning drive to an SSD for my daily backup using CCC a few months ago, I’ve noticed a huge improvement in speed. Previously, the backup process would take about half an hour, but now it only takes around one minute. That’s a remarkable speed improvement.

I’ve also been using an SSD for the Time Machine backup. I’ve had to rebuild my main drive a couple of times using the TM backup, and the process was much quicker than it would have been with a spinning drive. Additionally, finding and restoring files is much faster than before.