Pros and Cons of 16TB External Hard Drives

That article is a little dated, but reasonable.

For what I deal with, there are three general sorts of storage connections: NAS, DAS, and SAN.

Network Attached Storage, usually connected via Ethernet or Wi-Fi.

Direct Attached Storage, which can be USB, Thunderbolt, FireWire, SCSI, SAS, NVMe, etc...

Storage Area Network, which is usually Fibre Channel. This is a dedicated storage bus.

NAS, DAS, and SAN can be individual disks or SSDs, or RAID volumes, or virtualized storage.

NAS tends to be cheaper than SAN, but with higher error rates. SAN costs more, but with lower error rates.

Storage controllers can be present on most buses, either host-local, or served and external.

These controllers can present physical devices, or RAID volumes, or virtualized storage pools.

Some of these storage setups can mirror storage remotely.

Some configurations allow distributed shared write, others do not.

This whole storage discussion can get... gnarly. And complex.

etc...

You are much better off having a two smaller drives verse one large drive.

All drives fail—some new straight out of the box, this you never know.

Keep in mind a robust backup plan—

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.

Boot clone https://discussions.apple.com/docs/DOC-10081

How to use Time Machine to back up or restore your Mac: https://support.apple.com/en-us/HT201250

Use DiskUtility Restore feature https://support.apple.com/guide/disk-utility/restore-a-disk-dskutl14062/mac

note: >System Preferences>Security & Privacy >Privacy>Full Disk Access

unlock the padlock, press the + button and add Disk Utility

I usually run Promise Pegasus 6- and 8-bay RAID arrays for the folks that need that much storage, and those configured to RAID-6. RAID-6 avoids the messes of RAID-5 including the proclivity toward catastrophic failures when a second disk fails during rebuild, and RAID-6 doesn't consume as much storage as does RAID-1 or RAID-10. I've a number of Macs with from 16 to 64 TB configured, depending on requirements and array vintage.

If you want speed, then hard disk drives (HDDs) are not your choice.

A fast hard disk drive (15K RPM, big caches, fast I/O bus) will do between 100 and 200 I/O operations per second. You won't see those speeds in a stock Mac. And a decent SSD will quite commonly do a thousand times that rate, and you will find SSDs in a stock Mac.

For an overview, see the Wikipedia articles for RAID levels and hard disk drives. And SSDs, as those are wildly different from HDDs.

There are papers on empirical storage failure rates, of RAID levels, and the efficacy of and foibles of SMART data, that have been published over the years, but I don't have pointers to those papers handy.

https://www.cs.cmu.edu/~bianca/fast/

https://static.googleusercontent.com/mhttps://www.backblaze.com/b2/hard-drive-test-data.html

https://www.backblaze.com/blog/what-smart-stats-indicate-hard-drive-failures/

https://www.backblaze.com/b2/hard-drive-test-data.html

etc.

Entertainingly, as the capacities of HDDs increases, the likelihood of incurring a second and catastrophic failure arising during a RAID-5 rebuild approaches 1. And secondary failures are substantially more likely to occur during a RAID-5 rebuild, per empirical data.

Keep in mind RAID is not a substitute for a backup. Some RAID 0/5/6 levels permit faster read/write access to the slower hard drives and RAID 5/6 allows one/two drives to fail and still allow you to have access to the data while you replace the failing drive.

If you are going with 16TB+ of storage, then a NAS might be better especially if you have multiple computers which need access to the data. Synology makes a well respected NAS.

Personally I am not a fan of the Promise Pegasus storage systems. Our organization has had lots of trouble with them over the years. Plus the Pegasus units we have require using proprietary software to manage the drives. We also had major issues with Drobo as well.

Dexter5772 wrote:

If I may I'd like to ask a rather simple probably for you a boring question. If I am going to get an external drive to make local backups on a 16TB drive what do you think of the...

I use NAS arrays or hardware RAID storage arrays for backups, or bare drives, and not locally-attached single- or dual-disk setups, so not the right one to ask.

For disk purchases, usually WD HGST drives.

Avoid SMR drives; so-called shingled drives. This if you can figure out which ones are shingled, and which are not. Which isn’t always easy.

RAID-6, if the array is large enough to permit that.

A dual-disk setup is going to be two single disks, or striped RAID-0, or RAID-1. RAID-1 means ~8 TB from a 16 TB dual-disk setup. That’ll usually survive one failure. When striped RAID-0, that provides no reliability, and a failure of either drive will take the whole array offline.

There are a few Seagate 5 TB backup drives around in various installations, and they do work. Looks like 6TB is the sweet spot right now for those.

I prefer to avoid external storage that needs macOS drivers.

Some general (recent) reliability info, in addition to earlier links:

https://www.backblaze.com/blog/hard-drive-stats-for-2019/

What issues are you expecting?

Pro: lots of space for backups.

Con: External device hanging off the computer.

Don't know what else you are looking for.

Pro: You can put a lot on it.

Con: When the drive fails you lose a lot.

I prefer the Mercury Elite Pro Series from OWC:

https://eshop.macsales.com

Or you could buy an enclosure or a bay and bare hard drives.