External drive storage AND backup . time machine AND RAID

helennora wrote:

I think the best way to do this is to have a 4TB external drive and back that drive up with a 4TB time machine drive.

Sounds like a good plan.

Questions

Do I need RAID for the external drive or is a straight external drive sufficient here? I cant understand if RAID is just for disc failure back up our Fata backup or both.

Using regular external drives will work just fine.

Can I use a time machine drive on my external hard drive AND another time machine drive on my iMAC or do I use one time machine drive for both?

Time Machine can backup both the Internal drive and the photo library on the external drive.

Is this the best way of doing this?

It's OK, but I would also consider doing a daily or weekly Clone using CarbonCopyCloner or SuperDuper on a third external drive to be extra safe. https://bombich.com

Personally I use Time Machine and it drive always stays connected to my Mac. Then I use CarbonCopyCloner to make clones on another external drive. I generally only plug the clone drive in weekly to update it, but it always feel safer to update it right after adding a new batch of photos or other important work.

I think the best way to do this is to have a 4TB external drive and back that drive up with a 4TB time machine drive.

It's generally recommended to have TM drive that's about 2-3 times the size of the drive being backed up.

You can have both the boot drive and external HD backed up on the same TM drive. They all have different names and will be identified as such.

I use an 6 TB drive to backup my three drives totaling 2.5 TB. Gives plenty of room for lots of backups.

The Time Machine backup drive that you have, should still backup your Photo Library on the External Drive. But you should confirm that before you remove the Photos Library from your iMac. Which to me is the scary part and why I will always recommend a second backup of the Photo Library before removing it from the Mac.

For personal data like photos, a set of external drives is probably suitable. Use one as your primary working drive, and make regularly scheduled backups to another drive. These backups can run at night automatically when you are not using the machine.

If your data, or you are responsible for someone else's data like financial records during tax time, is used for a business or other mission critical purpose, where a drive failure happens like at 1 minute before the next scheduled backup was just about to occur, and the new created data that has yet to be backed up in that prior time interval is very valuable or irreplaceable, recovering from that kind of data loss could be expensive.

Then, a RAID-1 mirrored set of drives which essentially maintains an instantaneously synchronized backup of all the data from one drive onto the mirrored drive, might be a worthwhile consideration. The data is simultaneously written to both drives at once in a mirrored RAID-1. You can make a software based mirrored RAID-1 using the RAID Assistant in /Applications/Utilities/Disc Utility.app, or use an enclosure with that hardware based capability. When a hard drive fails, you just remove the bad drive and put in a new one, and you never have to shut down the machine or restore anything, the machine has no down time.

Glen Doggett wrote:

You can make a software based mirrored RAID-1 using the RAID Assistant in /Applications/Utilities/Disc Utility.app, or use an enclosure with that hardware based capability. When a hard drive fails, you just remove the bad drive and put in a new one, and you never have to shut down the machine or restore anything, the machine has no down time.

Unless the two drives involved in the software RAID are installed into the same external enclosure, then I do not recommend using a software RAID as it will most likely break due to differences between two separate external drives. If the physical drives which make up the software RAID are contained within a single enclosure in JBOD setup, then a software RAID will work much better. There have been numerous posts on these forums where users have had issues using an Apple software RAID on two separate external drives.

A USB enclosure such as this one gives you the option for built-in RAID1 support or you can enable JBOD mode and use Apple software RAID:

https://www.startech.com/en-us/hdd/s3520bu33er#overview-applications

This is just an example of one product. There are other respectable & reliable brands out there to choose from.

Also the hard drive manufacturers are changing how hard drives store data on the magnetic media so great care must be taken to make sure any hard drives used are not SMR (or Shingled Magnetic Recording) which have extremely slow writes and are not meant for use in a RAID. This information is not always properly displayed by the manufacturers or the retailers.

The RAID support is only to prevent down time if a drive fails and is not intended to be a "backup".