External Desktop or Portable for back ups? HDD or SDD?

We are in need of a new external hard drive for our back up and cannot make up our minds!

We’ve got the 2-4TB Western Digital Desktop and the 2-4TB Seagate Backup Plus Slim/Portable in mind. Budget is $100-$150.

It’ll stay mostly connected to a iMac 2019 512G SSD i5.

What are pros and cons to help us make a decision?
How is data regarding reliability of each?

And we are open to other product recommendations. Several folks here have pointed us to those mentioned above


My experience has been good with WD portable drives (My Passport, WD Elements, WD Easystore, etc.). A total of 6 (so far) ranging in capacity from 1 TB to 4 TB have been used over the years for Time Machine and Carbon Copy Cloner backups for my household’s two iMac computers and for external storage (DVR function) for a Tablo TV antenna/DVR device.

You can find these on sale periodically at Best Buy, Amazon, etc. It’s useful to monitor websites such as 9to5Toys.com for sales and promotions. My last 4TB drive was $79, I think. You don’t need the Mac-specific products; just use the Mac’s Disk Utility app on the standard PC-compatible drives to erase/format to the MacOS Extended/Journaled format. Takes less than a minute. I pay no attention to WD or Seagate apps or encryption capabilities or backup apps - I don’t know how they work and don’t trust them.

Regarding the portable vs “desktop” drive versions: The portable drives are powered from the USB port. The “desktop” drives require connecting to a power outlet with the usual “wall wart”. This is inconvenient, in my view, and requires extra cable clutter. The portable drives are smaller and can be attached to the computer stand using velcro.

Caution: the USB cables provided with both the portable and low-cost desktop drives are thin and fragile. If you experience any problems, particularly involving intermittent connectivity, try using a substitute USB 3.0 cable to troubleshoot the problem. I experienced this problem once a few years ago, and WD promptly supplied a new cable. It’s probably a good idea to have one or two extra USB cables available “just in case”. Here is my recommendation:
Note that this cable is much larger (thicker) than the USB cables supplied with the WD or Seagate low-cost drives. Be very careful when handling and connecting/disconnecting your drives using the thin USB 3.0 cables.

Regarding SSD vs. HDD: I don’t see the point for using the faster SSDs for simple backup. The HDDs using USB 3.0 are fast enough, and the cost is much lower. The more expensive as faster SSDs are better used when the speed is really needed - fast access to media files for video editing, for example, or use as an external boot drive.

Time Machine and Carbon Copy Cloner apps work better when the external drive capacity is larger than the internal drive capacity. For my iMac’s 1TB internal SSD drive backup I use 2- or 4-TB external drives. This ensures adequate overhead capacity for “versioned” backups over extended periods of time. The 4TB drives tend to be the “sweet spot” these days for price/capacity value.

It’s difficult to assess reliability. Reviews on Amazon and elsewhere are generally good, but varied. Some swear by WD, some swear by Seagate. My experience has been fine, and I’m comfortable since there is additional online backup using Backblaze. Another strategy is to use multiple drives in a periodic rotation backup strategy. The drives are so inexpensive that they can be considered expendable - just use them (with a good backup strategy) while they work, then discard them. I tend to use each drive for a couple of years, then store it in a safe for a while as a “deep-background/archive” and replace it with a new drive (bought on sale, of course).

The tech-loving geek part of me really, really wanted to buy a NAS (Synology) to replace my multiple port-bale-drive strategy. That would have been fun (for a geek), but expensive and time-consuming to learn to use all of the capabilities. I finally decided to take my own advice: “Don’t make your life harder than it has to be”. If it works, and it’s simple, it’s good.


I use a spinning drive for backup at school. My laptop hasn’t backed up there in about a month. This is solely due to the glacial speed of a spinning drive. The few hours I’m connected at my desk isn’t enough for Time Machine to figure out what needs to be backed up, and start backing it up. I back it up to an SSD occasionally and it is much faster. So it looks like I’ll need to leave the SSD at school, or buy another for there.

Backblaze publishes their drive reliability data. They have ~110,000 drives, so should be valid.

People often go on a rant about which drives are better or worse, but don’t realize some are made by the same company. For instance, Western Digital owns HGST, and Seagate bought Samsung’s hard drive business.


Here is a picture of the underside of my desk. I have a powered usb hub and three WD portable drives and a SSD to the left side of the picture. Everything is attached with 3M Command Strips and this setup has been there for over two years with no issues.


I have a Sandisk extreme portable SSD which so far has been fab! It’s really quick for time machine backups of my MacBook Pro. For me the speed is quite important as I have a laptop, therefore I connect the drive, do the backup and put it away again.

In your instance, it sounds like you could leave the drive connected for long periods therefore speed may not be such a such consideration. That said…
If this is your only back up: I’d advise against leaving it permanently attached to the computer. If someone breaks in & steals the computer with the backup drive connected then everything is gone. If your backup is hidden away somewhere then chances are you’ll still have that. That does increase the overhead of having to fetch disk, plug in, back up, unplug and hide it again. Ideally you also need an offsite back up be that cloud or having 2 disks and rotating them on a schedule.

As for reliability, as has been mentioned by others, there’s no one answer, some people swear by WD and have had nothing but problems with Seagate. For me it’s been the reverse, I have a Seagate drive for backing up a NAS, that’s been brilliant however a WD drive has been the only one I’ve had to fail on me. Again, the only thing you can do to mitigate the risk is have multiple backups across various platforms.

Yes and no, John. Keep in mind, for instance, they might test 80,000 WD drives and 4,000 Seagate drives, etc. If there are fewer failures with Seagate given the sample size that doesn’t mean more reliable. That said a good baseline for sure of what brands to get.

I think the question turns a bit on what kind of back up is proposed.

For a time machine back up, I think a self-powered 2.5" hard drive is a great idea, as long as its capacity is 1.5x the amount of data to be backed up. Bus-powered seems better to me than Yet Another Wall Wart and its attendant power draw, and the slowness of a 5400 rpm drive in a portable seems OK.

But for a clone of a boot drive, I think having an SSD make more sense. If you need to boot from it and continue working (say, under deadline), well, the 2.5" spinners are frustratingly slow, which apart from being inconvenient might well compound the stress felt from a failing boot disk.

For larger data sets you’re into 3.5" spinners. Best practice in my opinion is not to figure out the best odds of which manufacture maybe has the best reliability, but to have multiple back ups in different media, or at least with different brands, and in different places – since all hard drives will die eventually.

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@JohnAtl - This is a good point. Our home Macs are desktops, for which the portable HDDs work perfectly. Backup considerations for MacBooks would be different.

Regarding the Backblaze drive stats - these are fascinating, but difficult to assess for our use case. Backblaze uses enterprise-class drives, helpfully listing the actual drive model numbers. I have drilled around on internet discussion forums and disk drive reviews, trying to correlate these drives with those actually available to purchase. There are those who claim that some desktop-type consumer drives (Seagate Backup Plus or WD My Book desktop-type drives) contain certain disk drives that are enterprise-type drives - WD Red, for example. Checking further, others state that the WD drive enclosures contain “white-label” drives that may or may not be the same drives used by Backblaze. By the time that the word got out that the WD My Book enclosures contained WD Red drives, the drives were changed to generic “white label” drives. Similar story for Seagate. Bottom line - I found the Backblaze reports interesting in a general way but was not able to use the Backblaze stats to purchase specific hardware for my use. I ended up using portable (2.5”) drives, anyway, so the Backblaze stats for 3.5” drives were not applicable.

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That’s exactly what I do. SSD for CCC clone, spinning drives for other backups.

I want multiple backups, using at least two different methods, with one or more copies offsite. Currently using CCC and Time Machine but testing Arq as an alternative.

Hard drives are cheap, my data isn’t.

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Their published data are expressed as an annualized failure rate, which accounts for number of drives in use. More at the link.

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My apologies. I was basing it on this comment from Rdddir:

TL,DR: Seagates are failing more because they have been used more, not because they’re less reliable.

Assuming all drives have data read/written to/from them at the same data per unit time rate (TB/year, for example), then you can use the Drive Days/Drive Count to approximate how much usage each drive has seen.

In other words, a drive with a low failure rate because it’s seen less usage isn’t necessarily more reliable than one that’s seen more usage; it’s just been lucky to have been through less.

Therefore, the only “bad” drives in this table are the ones with below average usage AND above average failure rate.

Simple Excel shows that the only drive that fails the above criteria in the Lifetime table is the Seagate Exos X 12 TB (ST12000NM0007), which might explain its shockingly low (for the specs) retail pricing.

In fact, 2 of the 3 drives with the highest usage are Seagates, and Seagate is the only brand with more than 1 model having a usage time exceeding typical enterprise warranty (5 years, or 1826 days).

Note that the equal workload assumption above may be incorrect, but since Backblaze doesn’t tell us which drives are assigned to which workloads it’s difficult to say with any certainty. Hopefully all the drives have the same workload, because if they don’t that would basically make comparison invalid (workload has no effect on drive reliability below the drive’s workload rating, but the effect increases linearly above that rating) without knowledge of HDD-workload pairing.

For example, if the Exos X 12 TB HDDs are being assigned to workloads 2X their rating, they’re gonna fail at a much higher rate than other HDDs assigned to workloads below their rating.

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You have gotten good advice here, and I can only second the points that have been made.

I personally prefer WD drives, but that’s purely because I have had a few failures with Seagate external drives. That’s not based on real science as the sample size is of course way too small.

For a desktop, I would strongly argue in for the much less expensive and higher capacity spinning hard drives for backups. Like others, I have two bus-powered drives velcro’d to the under side of my desk, one for TimeMachine and one for a CCC bootable clone. For backups of this sort, SSDs are in my opinion an unnecessary expense, especially if you are backing up a desktop where the time for the backup to take place is longer. If you are backing up a laptop that will only be able to be connected to the drive for a short period of time (as per @JohnAtl), then an SSD may be worth the added cost, especially as your internal drive is probably smaller and hence a smaller external SSD would suffice. I favor drives at least 2x the size of the internal drive for both TM and CCC, although I actually use a much larger one for CCC since these bus-powered drives can be purchased so cheaply on sale, and I don’t delete the “safety net” backups.

Externally powered drives are, I think, helpful if you need a faster drive rotational speed as some are 7200 RPM drives while the bus powered ones are pretty much all 5400 RPM, and again I don’t think the faster rotational speed is needed for backups.

It is a reasonable point that have an SSD based clone is useful if you ever have to run your computer booted off the clone, but that to me is a relatively unlikely scenario for most of us. If your internal drive died on laptop or desktop you would like be taking it in for repair/replacement and hence the clone wouldn’t be useful anyway, When the repair machine is to be restored, yes the clone process going back will take a bit longer, but it’s a one time event.

However, if you are, for instance, frequently traveling with your laptop and need to be assured that if your drive were to die while traveling you could continue to work with the speed of an SSD, that might be a use-case for an external SSD clone. For instance, when I give talks, I will often bring a bootable clone of my laptop so that if my drive dies in transit I will not be stuck. (I also bring a spare copy of the talk on a USB stick and I could also grab a copy from BackBlaze or from my home machine via ResilioSync, but since the rest of the world is so Window-centric I might not be able to find a spare Mac to load my Keynote file). Thankfully I have never had to run out to buy an emergency Mac to give a talk!

Long winded, but hopefully helpful.


Dredging up the Backblaze drive stats topic again …

Looking back over the Backblaze stats over 2-3 years, some of the most reliable drives have been HGST (now owned by WD, as pointed out by @JohnAtl), I was inclined to track down a source for these and buy a number of them (2 - 4) for a tentatively-planned Synology NAS. Easier said than done. First, availability is limited. Second, these drives tend to be expensive. Third, reviewers of these drives repeatedly mention the noise generated, especially if there are multiple drives. OK … I can be patient and wait to find 3 or 4 drives, and I could probably choke and suffer through the cost. But no way am I going to allow multiple noisy disk drives to run continuously in my small home office.

Lesson learned: disk drives that are appropriate for enterprise use may or may not be suitable for home use.

Yeah, it seems like when I looked for them they (HGST) were only available in Costco-sized bundles.
I wound up getting 4x4T WD Red NAS drives for my Synology.

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I’m jealous. Do they work well? Quiet?

Yes, they are quiet. Not silent. I’m easily annoyed by noises, and they don’t bother me.
I’ve had them since January of this year, and haven’t had any problems with them.
Looks like they are $24 cheaper than when I bought them.

I agree for Time Machine, but not for a bootable clone. When you’re backing up, using an SSD for you’re bootable clone may seem like an unnecessary expense. When the time comes that you actually have to boot from that “bootable” clone, it’s going to be sooooo slooooow. I’ve run a system from a bootable clone on a spinning hard disk and it is downright painful. If you actually have to use it, backing up to an SSD for a bootable clone is more than worth the additional cost.


My external 1TB USB Time Machine disk is getting full. What do you guys do to transfer them to another bigger USB disk? Or do you just plug that bigger drive in and backup as a NEW Time Machine drives?

Just remove the drive from backups and start a new one. Keep the old drive for a while if you want access the old versions and deleted files, but eventually you can wipe the old drive and repurpose or dispose.

In this case, when plugging new drive to Time Machine, it will ask if you want to Replace or Use Both drive. I suppose Use Both is the better response as I might need to recover older versions of certain documents from the old drives, right?