Life expectancy of external backup drives

[joema2]

From experience, I would NOT rely solely on Disk Utility. I can't count how many times I've had failing drives, but DU found nothing wrong until it simply didn't recognize the disk at all anymore.

This is correct -- DU does not test the drive data, only the file system. This is a tiny fraction of the total contents. It is *very* possible to pass the DU "First Aid" test yet fail a restore due to a bad block.

The following scenario can easily happen:

(1) You have a problem requiring full-system restore from a Time Machine backup
(2) Since this erases all drives being restored, you first run a DU First Aid on the Time Machine backup. It says no problems found.
(3) You commit to the restore, which erases all drives.
(4) After 5 min of restoring, the Time Machine backup encounters bad blocks and halts.
(5) You have erased whatever you had before, and now the Time Machine restore won't complete.

Since neither Time Machine nor Carbon Copy have a validation function, there is no way to inspect the backup quality except by restoring it to another machine.

The ScannerZ utility can force a read of the entire drive to verify all blocks are still OK: http://scsc-online.com/Scannerz.html

DiskTester can read all files on a volume to verify they are accessible: https://diglloydtools.com/disktester.html

However since drive space is relatively cheap, it might be quicker to simply clone the drive in question. That doesn't require specialize diagnostics, runs very fast and makes another copy of the data.

 

[imanidiot]

Assuming we're talking about a backup strategy here, the golden rule is to have 3 backups on 3 different types of media (disk, tape, maybe internet) in 3 different locations. I would replace one of the working WD drives with a totally different drive from another vendor (see backblaze report). Take the good but replaced WD and put it in off-site storage. This way you are actively backing up to two drives from different vendors with two different life expectancies. You don't run the minuscule risk of both drives failing at the same time at the end of their life.

I did a totally unreliable calculation of how many backblaze drives failed a day from the last 90 day report. Looks as if they have about 4 drives a day fail and they are not particularly worried about it. In other words plan for failure so when it happens you don't sweat it.


As above run 'em till they fail. Since you are alternating backups between two drives it's not a problem if one dies.

Great advice. Thank you.

 

[HDFan]

Since neither Time Machine nor Carbon Copy have a validation function, there is no way to inspect the backup quality except by restoring it to another machine.

As above if you don't test your backups regularly you can't be sure that they are not corrupt. I recently did a restore on a large external disk (~14 TB) with CCC. Just to make sure I ran CCC two times, and on the second try it transferred another ~TB or so with no changes having occurred on the source disk. If you know that you are going to be wiping a disk I'd run CCC at least a couple of time when making the backup. That gives you a little validation that at least CCC thinks the backup is OK.

TM backups are more problematic and I have tried to do restores a number of times and the TM backup failed due to corruption. I've lost entire TM disks as well. If you're doing a complete backup/wipe/restore I would use one of the disk utilities such as DiskWarrior to verify the TM file structure. And, of course, try restoring a file after whatever repairs it makes before wiping the disk.

 

[joema2]

As above if you don't test your backups regularly you can't be sure that they are not corrupt.

The problem is neither TM nor CC have built-in validation of backups. By contrast Acronis can validate an old backup by reading every block plus internal Acronis data structures to ensure it's still good. It's a built-in feature, so it's easy to use.

How many people are going to do a full test restore of a TM or CCC backup just to validate it? That takes an entire spare disk (or drive array) equal to the backup size. Even fewer are going to use some specialized commercial utility like ScannerZ, DiskTester, Drive Genius or Tech Tools. Only those (or similar) can truly validate the disk because only those read all blocks in the files. DiskWarrior is a great program -- I have it -- but it does not generally validate anything besides file system structure which is a tiny part of the disk data. It has a hardware test but only works on certain types of disks.

One lesson is don't ever wipe out a current hard drive trying to restore from a backup which is not verified. Another lesson is backups are only good to the extent they are verified. Unfortunately few people understand that or how to perform the verification...[/QUOTE]

 

[MacRobert10]

I use a dual SSD RAID 0 enclosure to hold all my development work, and then use Time Machine to do backups. Once a month I'll do the following:

• Do a scan on the entire TM backup with Scannerz to ensure it's still good.
• Clone each of the development volumes with Phoenix (comes with Scannerz) to another drive (more on that later).

Basically when cloning I erase the volumes on the drive I use for cloning and then clone the existing stuff from the RAID unit over to it.

Here's an interesting tip for anyone looking for a Thunderbolt drive enclosure for an SSD: Buy a LaCie 1TB Firewire/USB 3 drive, pull the drive out, and then you can put an SSD in it. The RAID unit I'm using is a USB 3.0 unit and it's still faster than a standalone Thunderbolt drive, but not by much. I've seriously thought about getting another LaCie, putting the two SSDs into each of the Thunderbolt housings, then configuring it as an Apple RAID 0 unit. With RAID 0, backups are critical by the way. The drive that I use for doing the clones of the volumes is the drive I pulled out of the LaCie Thunderbolt/USB 3.0 enclosure.

Seagate used to make some type of Thunderbolt adapter and there selling for as much as $250 now. The LaCie can be picked up for $150, and you then have a backup drive for your SSD if you go that route.