Re: another Time Machine thread - still need SuperDuper?

On Nov 6, 10:47 am, demp...@xxxxxxxxxxxxx (David Empson) wrote:
ric <publicm...@xxxxxxxxxxxxxxxx> wrote:
Been thinking about Time Machine - bear with me as I've not got
Leopard yet.
I'm planning on partitioning a large external USB drive, and using
that with Time Machine.
I was thinking of making the partition the same size as the Mac's boot
drive that I'm backing up, but thinking about it, that's a bit daft,
isn't it? Presumably you need boot volume size plus a fair margin (am
now thinking 150% or so) for the deltas.

The exact size will depend on what proportion of your original data is
changing and how often, and on how long you want to keep backups.

It will be hard to judge this sort of thing until everyone gains more
experience with Time Machine, and someone who has a similar usage
pattern to you can give approximate figures on the amount of backup data
they are generating. This will be hard to determine, because each Time
Machine backup looks like a complete copy of your data, but is only
using additional disk space equal to the changed data. We might need
some new third party tools to allow better analysis of Time Machine
backups.

Depending on how often and how long your computer is running, Time
Machine wants to keep up to 24 hourly backups then a month's worth of
daily backups. That's between 30 and 54 "recent" backups, each
containing all files that have changed since the previous backup. After
that it will keep one backup per week, for as long as possible (until
your drive gets full). That works out to be around 80 to 100 incremental
backups after a year.

It is reasonable to expect the weekly backups to be larger, as more
files will have changed. Daily backups will generally be smaller (except
when something big like a system update gets installed), and hourly
backups will be smaller still.

There will be one complete backup (most of the files on your disk,
excluding caches and other temporary files). If you assume that on
average you get about 1% of the files on your hard drive (by size)
changing or being added every week, then after a year you would have
needed in the order of 50% additional storage, plus somewhat less for
the daily and hourly backups (maybe another 10% in total). That suggests
a backup disk about 1.6 times the size of your orignal might last a
whole year before it starts throwing away old backups.

If 10% of your files (by size) change every week, then you would need a
backup volume which is about six times larger than your current used
space if you wanted to keep a whole year's backups.

I'd be inclined to go for something in order of twice the amount of used
space (or potentially used space) on the primary drive. If your boot
drive is 160 GB and your peak usage is in the order of 140 GB, a 250 GB
backup drive should be good enough and a 320 GB should be plenty for
most people. If you are expecting the total size of changed or added
files each week to be large, then you might need a larger drive.

The major thing to watch out for is very large files which change in
small ways. For example, if you use Entourage, its entire mail database
is stored as a single file, which can be well over a gigabyte. Any
e-mail arriving will change that file, requiring Time Machine to do
another full backup of all the e-mail. If you are using Apple Mail, this
won't be a problem, as each message is stored in a separate file.

A similar problem is any virtual machine (Parallels Desktop or VMware
Fusion): booting into Windows will modify the virtual drive image, which
will then need to be backed up again. This is likely to be a 6 GB or
larger file.

If you need to deal with files this big, you might need to exclude them
from the Time Machine backup, and make alternative arrangements for
backing them up.

This may require keeping a separate copy of those files manually, so
factor that into your calculations for backup drive size.

Now, say the worst happens. My Mac's internal drive dies, or the
machine gets nicked. I've a backup of files on my external drive from
TM, and the suggested recovery method is boot off the Leopard disk,
start TM and recover from there, yes?

Yes.

You can also use Migration Assistant to migrate data from a Time Machine
backup to a newly installed system.

Can you recover the whole disk to a certain date?

I haven't checked, but I expect you can pick any backup that Time
Machine has kept.

What happens if you want to recover data to another Mac - is this
possible?

Yes.

Not sure a Leopard disk as supplied with a new MBP (as
opposed to a retail disk) would boot on, say, an iMac or MB...

A retail Leopard disk will boot all current Intel Macs, and supported
PowerPC Macs. I expect it also supports the just released MacBook
models, but might not work on the next new Mac model to be released.

After that point, recovering from a Time Machine backup on a new
computer might be a little trickier. You won't be able to do a direct
restore onto the new computer, because the system from the old model
might not boot on the new model.

In this case, you use Migration Assistant instead. When setting up the
replacement machine (or installing Leopard on one), the setup assistant
will ask if you want to migrate data from another Mac, or a Time Machine
backup. This will allow you to recover your applications, user accounts
and other files (but will leave the old system behind).

You can also run Migration Assistant at a later stage and do the same
thing.

Basically, I'm wondering if I treat TM as a handy automagic file-level
backup and supplement it with an additional SuperDuper image to a
separate partition as well.

I'm intending to do that, mainly so I have a complete backup
(SuperDuper) to supplement my almost complete backup (Time Machine) -
I'll be excluding some large files from my Time Machine backup.

The SuperDuper backup will only be updated occasionally: I'll be relying
on Time Machine as my primary backup. I'll update the SuperDuper backup
at points convenient to me, e.g. just before installing a system update.

I have two identical hard drives (500 GB each) which I'll be using
mainly to back up my MacBook Pro (160 GB), each with a clone plus Time
Machine (two partitions). One hard drive will be kept at work and the
other at home, so I always have an off-site backup.

The only hassle with this setup is that Time Machine has to be manually
configured to switch backup drives. I'm hoping I can automate that with
something like AppleScript, or Apple makes it easier. Otherwise I'll do
something like use one drive for a month then swap them over, or maybe
arrange to do evening backups at home at least once a week while doing
daily backups at work, and occasionally rotate the drives so that they
get roughly even use over time.

If I did this, I'm not 100% confident on being able to restore from a
SD clone that's on a separate partition - does this cause problems?
If I have an SD clone on one of several partitions on a disk, what do
I need to do to ensure it's bootable? Does the magical blessing of it
happen during the backup via SD?

SuperDuper backups are bootable, as long as you have them on a drive
with the correct partitioning scheme, and the drive itself is bootable
(some external drives aren't - this is a limitation of the drive
controller firmware).

The only partitioning scheme restriction is that a PowerPC Mac can't
boot from a drive using GUID Partition Table. It has to be Apple
Partition Map.

An Intel Mac can boot from either scheme, but the Mac OS X Installer
won't let you directly install a system on an APM drive from an Intel
Mac (you can clone a bootable system onto an APM drive).

Another restriction is that a PowerPC Mac can't boot from a USB drive,
but is OK with Firewire. An Intel Mac can boot from either.

--
David Empson
demp...@xxxxxxxxxxxxx

Some great info here, thanks. So using Migration Assistant from Time
Machine backup's definitely possible?
WRT to SuperDuper backups - it's the "correct partitioning scheme" bit
that I'm concerned about. Assuming the drive I've got is capable of
booting an Intel Mac (I *have* got my head around the issues there, at
least!) then am I right in thinking that I'd just partition the drive
as HFS+, use SD to backup to it, and that's all that's needed to make
it bootable? The Intel Macs don't have any caveats such as only
booting off 1st partition on the drive etc?

I suspect that so long as my *data* is OK, I can put up with a
reinstall in the event of anything really bad happening. So TM may be
enough in itself, bearing in mind the restore from Migration
Assistant. I'd not thought about this before, but I could restore
apps this way, as well, I guess...

Shame that the backup over the network feature was removed - I'd love
to be able to have TM work in the background to my NAS...

Ric

.

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