New 27" 5K iMac question

[NateS]

Nice reply^^ I wrote mine before reading this.

Ok I'm still learning so let me see if I understand this. Time Machine has its one drive, is 1TB big enough for time machine? Then I should get another drive to back up the Time machine drive? I must not be understanding fully. Because that seems very excessive and costly. I do plan on using SuperDuper. as I would like an exact clone of my drive. …

My main concern is having an exact clone of my system so I can be up and running as quick as possible. Not much else will be stored on the internal drive other then APPS.

Allow me to clear up a misconception and perhaps provide a useful analogy.

I am not suggesting that you make a backup of Time Machine. Both the Time Machine disk and the SuperDuper disk should be making their backups from your original data disk.

For an analogy, let's say you have a nice new automobile and sadly it gets in a crash. Your ins. co. sends you to the dealership and first you stop at the parts department. Time Machine is the parts department and the manager says:

"We can replace the parts that are damaged or fell off the car. Or, if you want a total replacement, we can build you an entire brand new car from all our parts, but it will take quite awhile - how long do you want to wait?"

So you go up front to the new car dealership and the dealer says:

"Here's a brand new one exactly like yours. You can drive off in it if you'd like!"
The new car dealership is like SuperDuper.

Maybe this will help. That's why it is wise to have both, as different circumstances as to the extent of your crash or deletion, and how soon you need to get going again, will determine which is a wiser method of recovery.

Best wishes, Nate

PS - In addition, Time Machine keeps different versions of each file, so you can go back in time to an earlier version if you have screwed up the current one on your data disk; whereas SuperDuper always deletes and replaces older versions with the most recent one at the time of its latest backup. Different calamities call for different rescues.

 

[MacInWin]

That means you are advising new Mac users on a forum where they come for advice that Fusion Drive is so unreliable that backups are more important on that drive type. That is misleading, especially to new people.

joema, again you try to put words in my mouth. I did not say, anywhere, that Fusion drives are "so unreliable..." All I said was the scientific fact that fusion drives are more prone to failure than their component parts are. But let me ask you, is a backup of a 98% reliable drive more or less important than the backup of a 97% reliable drive? Based on the statistics available from the articles, if I have 1000 fusion drives and 1000 spinners, over the year I would expect 20 of the spinners to fail and 30 of the Fusion Drives. Is that enough difference in risk to consider? That's a decision the user must make, but it is a decision that needs to be made in the light of the statistics, not marketing.

The bottom line is, backups are important, period. And the less reliable the primary storage the more important the backups are.

That is fine and such facile reasoning may eventually be proven correct, regardless of the current lack of evidence. However all the new Mac users should understand there is so far no evidence that a Fusion Drive has significantly worse real-world reliability than the same size SSD, and certainly not sufficiently different to change their backup policy.

Again, you ignore the article YOU cited. There is evidence to consider, if you will consider it. Also read this and this. I think that the idea of the fusion drive being less reliable than the individual components is "proven correct," even if you don't want to hear it.

And anybody who fails to have a backup policy is just stupid, IMHO. The reliability of drives of any type notwithstanding, if you think it's important enough to store on the drive, it should be important enough to back it up. Otherwise just trash it and move on. Drives fail. That's life. And when you merge them, as in a Fusion Drive, the probability of that failure goes up. That's also life.

So, can we leave it that we agree to disagree? You obviously aren't going to be swayed and neither am I.

 

[joema]

...I think that the idea of the fusion drive being less reliable than the individual components is "proven correct," even if you don't want to hear it. j...

We need to be extremely clear here -- I posted the equation showing that fusion drive is less reliable than the individual components. It is a series network issue. Of course it is less reliable -- than the individual components.

But the proper comparison is not Fusion Drive vs the individual components. It is Fusion Drive vs the same-size SSD, which by necessity uses different components. They are made with different processes, different manufacturing batches, different QC, different peripheral support components.

The fact that a 1TB Fusion Drive has less mathematical reliability that those exact same un-fused components in parallel has no proven relevance to the available purchasing options actual buyers are likely to exercise. The huge historical variation in SSD reliability shows that. Some have had 66% failure rate, others quite low. Some HDDs have had high failure rate, others low. This can easily swamp the difference between FD and any same-size non-FD, since you can never guarantee the reliability of the individual components will be the same.

 

[MacInWin]

And there you go, making crap up again. I realize you posted a formula, but it's the same formula I've been using all along so we agree on the science. But I've never compared a 1Tb Fusion drive to a 1Tb SSD. Although, if you want me to, if you assume a 1Tb SSB and a smaller SSD (like you would see in a Fusion Drive) have the same failure rate, then the Fusion drive will be less reliable, using the formula you and I agree on using. It's still two devices and added complexity. In practical fact, one of the articles I provided said that larger SSDs have lower reliability, at least at the time of the article, so a 1TB SSD may, or may not, be more reliable than a 1Tb Fusion drive. But that's not the comparison we started with.

The proper comparison that I have been making all along is between a single Fusion drive and the same components in parallel. If I have a single Fusion drive, 1Tb, made up of, let's say, a 256Gb SSD and a 750 GB spinner (It could be plus or minus a bit, but this is all theory, right? I read one article that says the SSD is only 120GB, but that really doesn't matter, it's small in any case.) and now I put those same two devices in the same computer in parallel, boot from the SSD, store data on the HD. If we assume the SSD is 99% reliable and the spinner is 98% reliable (according to the other websites we've cited), then in the Fusion Drive, using your formula, the reliablity of the Fusion drive is 97%, which means you have a 3% possibility of losing EVERYTHING on the drive. Now let's look at the system with two drives in parallel. The probability of losing everything is lower, because now you have to lose BOTH drives to lose everything, which is calculated at .02 * .01, or .0002, or 0.02%. Now you CAN lose the boot SSD (1% probability) or the data spinner (2% probability) but in neither of those cases have you lost EVERYTHING, which is what this discussion is all about. So the difference between the two "lose everyting" options is 3% and 0.02%. And if I lose the SSD, I don't care as much because I can resintall the OS and Apps that were on there and all my data files are still there on the spinner.

Now, in practical matter, maybe that difference in risk isn't significant to you, but to soemone else, maybe it is. With the split SSD/HD system with the lower probability of failures to lose everything and a quick boot/application start time, the only performance hit is in reading and writing large data files from the spinner. But the probability of losing those data files is reduced from 3% to 2%. Is the performance trade-off worth the risk? That is a decision that is up to the buyer. (Note also that the cache on the Fusion drive is only 4Gb, so files larger than that get the same performance hit anyway. But that's a topic for another day. Let's keep this about reliability.)

That's how it is. And that's why I don't have a fusion drive and why I won't create one on my system.

You can do what you want. Readers of this thread can do what they want. I'm not misleading anybody when I say the bottom line is that
1) Backups are important, really important, no matter your decision.
2) Fusion drives are less reliable than straight drives because of the complexity.
3) The difference in reliability is, for most folks, not something on which you can change your backup plan. See #1.

If you are interested, in my MBP I have an SSD from which I boot and on which I store my more critical data (480Gb) and a second SSD on which I store less critical data (also 480Gb). I have the boot SSD backed up with CCC to a spinner clone and a Time Machine spinner, and the data SSD backed up to a third drive. That way everything has a backup and my critical data has two backups on separate drives.

I'm thinking about getting a 4Tb drive to use for a redundant backup of all the backup drives. Yes, I'm paranoid about data loss. Which goes back to my original post, I don't trust Fusion drives at this point. If they somehow show greater reliability, then I'll reconsider my position. But I'll still have multiple backups.

 

[MacInWin]

chas_m, resorting to ad hominem attacks indicate that you have no logical argument on your side anymore, which in turn means you concede my logic is unassailable. Thank you for that concession, even if you didn't intend to do so. And if the difference between the failure rate was 0.00001 and 0.00002, as you said, it would be relatively meaningless. But it's not. The difference in the real world is between 3% and 0.02% which is not double, but 150 times. In the real world, the probability of losing everything on a fusion drive is 150 times what it is if the same two components are un-fused and run in parallel. Somehow that seems sort of meaningful, at least to me.

I'm done here. (But I bet you or joema can't resist one more shot )

 

[chscag]

And with that, this thread is done.