TimeMachine est backup size larger than whole drive!
 

Are Time Machine's estimated back up sizes numbers we can trust, or should ignore?

My drive with OS and files is about 400 some GB; the entire drive itself is a 640GB drive, yet Time Machine tells me the estimate for a full back up is 933GB!

How does it arrive that that figure?

thank you for any clarification on this.

a

Do you have any external drives connected to your Mac? You may need to add them to the Time Machine exclusions in System Preferences > Time Machine > Options.

Here's what I have...the 640 that came with the machine and 2 1-TB Hitachis.

You're saying TM is adding up ALL the files everywhere? This suggests TM can back up from one non-boot drive to another, is this correct?

a

Yes, it can. Add one (or both) of your external drives to the exclusions then start backing up to see how much space Time Machine indicates a full backup will be.

I see...good to know..I tried to investigate this angle some time ago but didn't get much sense of what TM would do..very understated in its power...

a

It's understated and it's got limitations. So it can back up loads of stuff and provide access to past versions, but (as was discussed in another thread) it doesn't provide bootable backups.

Just to give you some ways of thinking about things, I do exclude system files from Time Machine. To me, it's not worth wasting the GBs because if I have an issue I'll fix it with either one of my clones or using the Recovery partition. I also exclude applications which are regularly updated and readily available. iTunes would be an example of this. Between all the updates and its size, it doesn't seem worth it to me to blow a GB or so per year backing this up.

Instead of a Downloads folder, all my downloaded and temporary files get routed to a specific volume. I exclude this from Time Machine simply because I have no need for lots of stuff here to be backed up (email attachments, applications I try, PDFs I create to send to people, etc.). Mind you, this temporary-file repository still gets backed up as part of my daily cloning, but I try to minimize what goes on my Time Machine volume since Time Machine creates space when needed by removing the oldest files. Unfortunately, you're only notified after the fact.

None of this is to say you should do the same types of things. Some might say I'm giving more effort to this than necessary. I just mean to note there are ways to optimize for yourself what Time Machine backs up that you may want to consider.

As of 10.7.2, local (non-AFP) Time Machine backup disks are bootable. When you do so, you boot into an OS X recovery system, where you can perform a Time Machine system restore, etc.

The Recovery partition can let you recovery certain parts that have gotten corrupt or otherwise hosed?

a

Lion and Mountain Lion each have the Recovery partition which can re-install the OS after downloading it from Apple. The Time Machine recovery partition which Mikey-San mentioned (thankfully, since I forgot about it, which is made worse since I think he was the one who first informed me of its existence), provides a means of re-installing a working system from a Time Machine backup which, as he noted, must include system files.

In simple terms, there are two types of Recovery partitions; One is installed by the OS and can connect to Apple to re-download the 10.7 or 10.8. The other is available in conjunction with Time Machine if you've included system files in your Time Machine backups, and this will allow you to restore your system.

wow...that is the sweetest news I've had all week! the current TM options I have selected includes system files but not apps...which I guess I can add to get a restorable OS plus all my apps...

Safe to say that the system you restore is only as "healthy" as the one you back up, right? So if you have a system with issues, you'll back up the issues, too.

a

We'll need to research that. I've never used the Time Machine recovery system, so I don't know if it allows you to pick a point in time from which to restore. But what you described is definitely a concern with clones. If you have a serious issue and clone the affected drive, that's not exactly what you want for data security. With issues like this, not to mention the fact that hard drives die, you can see why data redundancy is important.

So, this is also incorrect. Time Machine backs up the standard recovery system, and that's what you boot from when you boot from a Time Machine disk.

The recovery system is also backed up even if you aren't backing up normal system files. That way, you can still boot to your Time Machine disk in order to reinstall OS X and then migrate data from your backup.

Edit: I don't recall noting that you have to back up system files in order to get this functionality. Did I previously?

My mistake, confusing this thread with the other one acme started that's also about Time Machine.

If I boot and hold the Option key (running 10.7.4), is this the volume called EFI Boot which has the Time Machine icon?

Should be.

Thanks, Mikey-San, for this and for correcting my mistakes above.

Is using TM hard on the drives involved in making all of these daily/hourly, etc, backups?

trying to protect data and my wallet at the same time!

:o

thank you!

a

I've tested Time Machine restores every which way till Sunday. It starts off by telling you it's going to erase one of your volumes and restore it from backup, but first it will need three pieces of information from you:
a) Which disk volume do you want to restore onto?
b) Which backup do you want to restore from?
c) Which snapshot on that backup do you want to restore?

Then it asks those three questions.

Then it tells you what exactly it's going to do, reminds you that it will have to erase the destination volume before restoring to it, and gives you one last chance to OK or cancel the whole thing.

Then it does it.

If the restored volume is bootable, it asks whether you want to make it your default boot volume. If you boot from it, it asks if you want it to continue backing up this volume up to the same TM backup you just restored it from, as if this was the disk it had been backing up to that backup all along.

Snapshots are identified by the name of the machine, the name of the volume, and the date/time. There is no required relationship between your current OS version and the version being restored. You are reminded that you should always restore to the same machine you backed up from.


As of 10.7.2, every time you do a TM backup to a local disk, Time Machine makes sure there's a current version of a file named tmbootpicker.efi at the root level of the backup, and blesses that as the startup file.

As nearly as I can figure out, tmbootpicker.efi has the same code found in the firmware of modern Macintoshes that handles the ⌘R combination at startup. What the code does is look for any "Recovery HD" partition (I would presume the latest if given a choice) or, if not finding any, downloads one from Apple into RAM.

The relative sizes are instructive: tmbootpicker.efi is only 116KB. Recovery HD is 650MB. Mountain Lion's InstallESD.dmg is 4.0GB. We can assume each has been compressed to within an inch of its life, so none of them can contain any larger file in the sequence, not even with very clever compression.

However you get to Recovery HD, booting into it reveals that it consists almost entirely of a single compressed HFS+ disk image, named /com.apple.recovery.boot/BaseSystem.dmg. That BaseSystem.dmg (451.3MB for Lion, 448.7MB for MtLion) is what's actually booted from (possibly after being copied to RAM, freeing up the drive itself to be repartitioned by Disk Utility if needed).

Thus, the real significance of the TM volume being bootable is that it brings the benefits of Lion Internet Recovery to users whose Macs are new enough to run Lion (or MtLion) but not new enough to have LIR in their firmware. It would behoove users to arrange to also have at least one copy of Recovery HD always available, ideally on the TM volume itself, to forestall a 650MB download.

I have verified that I can do a full TM recovery, to any version of the OS I have backed up (from 10.6.8 to 10.8.0) with no internet connection. (I did have Recovery HD available in all tests.)

One other comment about Time Machine restores: they're fast. I can restore a volume from TM faster than I can re-clone the same volume using SuperDuper. (Tests were run with all volumes locally attached, copying USB2.0 to Firewire800 so as to avoid competition for the channel.) I don't recall the actual times, but the differences were not really enough to worry about. I mention this only because I've seen people opine that surely TM must be slower than SD, apparently without actually testing.

sorry to bump this question, but I have a concern whether Time Machine use causes an increase in wear on the drives involved in making the constant backups.

Is this the case?

hourly backups after little/no work has been done can't involve moving much data, but I've I'm working hot and heavy with many photoshop files, or editing video, I can see it running into serious amounts of data and therefore more work being demanded of those drives.

Thank you for any information on this!

a

If you modify a file on your system disk, a copy gets made to your Backup disk.

In other words: no more wear and tear is done to your backup disk than is done to your system disk by doing what you do.

OK, but that backup happens at the next scheduled (hourly?) TM back up..

So, you create or modify, then x-number of minutes later, dep on how far that back up is away, another copy is made. To me, that sounds like twice the HD activity. Once for what you did, a second time when TM backs it up.

Is that a correct way of characterizing it?

a

If you modify the file in the next hour, then you will, most likely, re-write the entire file on your system disk. And then TM will back it up. So we're still on parity here. The difference is that TM didn't overwrite the old file.

If you don't modify it: TM does NOT make a copy.

And, TM copy writes to the TM volume, not to the boot drive.
Outside of your initial TM backup (which can take a significant amount of time to complete), normal TM activity is not too involved, compared to the normal read/writes that your system does outside of TM.

OK...both your replies are very illuminating...

So, even the major backups will most likely be lighter on the hardware than the initial, unless I do more work, create more files and make more changes equalling to more space and file size than the original..

maybe the first TM back up is a huge gulp, thereafter...little sips?

a

That pretty much sums it up.

What, no creaky bridge here?

Wear & tear on a spinning drive is of minimal concern until it's excessive (like defragmenting)

Extensive video editing that changes the original files (check the modified dates) will fill up your backup drive in record time - in this case good practice is get a good external*, put the video files on it (and redirect the editor's scratch space there) and exclude this drive from TM. You typically don't need a backup of video workfiles as you should still have the originals in the camera.

* full-size drive, FW800 or Thunderbolt case. A pocket USB drive would be a very poor choice. A 15,000 rpm drive with eSATA or Tunderbolt would be excellent.

I want to correct an egregious error in what I posted.

In addition to creating the tmbootpicker.efi file, Time machine also creates a folder Backups.backupdb/.RecoverySets/0/com.apple.recovery.boot on the backup disk, and populates it with the same data found in the com.apple.recovery.boot folder found at the top level of the recovery partition. In particular, both folders contain BaseSystem.dmg, which is what you actually boot from when you boot into recovery mode.

Thus, a Time Machine backup volume is bootable and completely self-contained, not requiring the existence of a "Recovery HD" partition anywhere else, nor on having Lion Internet Recovery in firmware. Booting into it has the same effect as booting into a "Recovery HD" partition without actually needing one.

All of this applies when backing up to a directly-connected local disk. I don't know if TM puts this same information on a Time Capsule backup, nor if it's even possible to boot off a Time Capsule


I had searched my Time Machine backup volume for an equivalent to Recovery HD, and when I couldn't find one on the volume assumed that tmbootpicker.efi was pulling the information from elsewhere. Only a "real" Recovery HD was large enough to contain all the code it was using. Perhaps what threw me was that at the time I didn't know what the innards of Recovery HD looked like, and must have dismissed com.apple.recovery.boot as being too small. (It's 468MB, compared to 650MB for Recovery HD.) Since then, I've explored inside Recovery HD, and see that it is in fact complete, with most of the size difference being just room reserved for expansion.

Sorry for posting inaccurate information.