Time taken for back-up

[Scott]

Basic question I know, but why does a back-up using Norton Ghost take
more than two hours? I thought computers carried out millions of
calculations every second. Is it to do with the writing time to the
back-up disc?

 

[John Williamson]

Basic question I know, but why does a back-up using Norton Ghost take
more than two hours? I thought computers carried out millions of
calculations every second. Is it to do with the writing time to the
back-up disc?

And the reading time from the original, and the speed of the data
transfer between the two.

How much data do you have? I have half a terabyte here, and the first
backup took all night, with incrementals taking anywhere from a few
minutes to an hour or more, depending on how busy I've been.

 

[Jeff Layman]

And the reading time from the original, and the speed of the data
transfer between the two.

How much data do you have? I have half a terabyte here, and the first
backup took all night, with incrementals taking anywhere from a few
minutes to an hour or more, depending on how busy I've been.

Add to that, if you are doing it, the time taken to check and verify
that the backup is accurate.

I use Easeus ToDo Backup free, and that takes about 30 minutes to make
an image of my laptop HD (about 50GB) on an external HD via USB2.

 

[Ken Blake]

Basic question I know, but why does a back-up using Norton Ghost take
more than two hours? I thought computers carried out millions of
calculations every second. Is it to do with the writing time to the
back-up disc?

Calculation is not a significant factor. The time it takes is largely
dependent on three things:

1. How much you have to backup. This can vary enormously from one
computer to the next.

2. The speed of reading from the disk you are backing up.

3. The speed of writing to the backup disk (and note that if the
backup disk is external--as it should be--it's particularly slow).

But for most people, the speed of backing up is not very significant.
Start it before you go to bed at night and it should be done in the
morning. How long it took seldom matters.

 

[Scott]

Calculation is not a significant factor. The time it takes is largely
dependent on three things:

1. How much you have to backup. This can vary enormously from one
computer to the next.

2. The speed of reading from the disk you are backing up.

3. The speed of writing to the backup disk (and note that if the
backup disk is external--as it should be--it's particularly slow).

But for most people, the speed of backing up is not very significant.
Start it before you go to bed at night and it should be done in the
morning. How long it took seldom matters.

Why does the reading speed matter? Surely reading is faster than
writing and the computer can do both as the same time?

 

[Dave]

Calculation is not a significant factor. The time it takes is largely
dependent on three things:

1. How much you have to backup. This can vary enormously from one
computer to the next.

2. The speed of reading from the disk you are backing up.

3. The speed of writing to the backup disk (and note that if the backup
disk is external--as it should be--it's particularly slow).

But for most people, the speed of backing up is not very significant.
Start it before you go to bed at night and it should be done in the
morning. How long it took seldom matters.

Agreed, I use Macrium Reflect free version. There is an option to turn the
machine off after backing up. Good idea to always verify.
Most of these image programs will only backup sectors in use and use
compression which probably adds some time. I partition the drive, system
and installed programs on C:, other stuff on D partition. I only image C:.
With today's huge external drives it's just as easy to simply backup the
data partition as is. I use winmerge to keep things in sync. Lots of
others out there.

 

[John Williamson]

Why does the reading speed matter? Surely reading is faster than
writing and the computer can do both as the same time?

The data will move at the speed of the slowest link in the chain, less a
bit for overheads. There's also a speed hit caused by reading the data
back off the backup disc to verify it by comparing it with what the
computer thinks it just wrote. You can make backups a lot quicker by
omitting this step, but you then have no way of knowing if the backup's
good or not.

I know a number of people who've found this out the hard way.

 

[Scott]

The data will move at the speed of the slowest link in the chain, less a
bit for overheads. There's also a speed hit caused by reading the data
back off the backup disc to verify it by comparing it with what the
computer thinks it just wrote. You can make backups a lot quicker by
omitting this step, but you then have no way of knowing if the backup's
good or not.

I know a number of people who've found this out the hard way.

So in practical terms the speed of writing to the external disc is the
determinant?

 

[John Williamson]

So in practical terms the speed of writing to the external disc is the
determinant?

Usually, yes. In my experience, the speed is normally limited by the
interface, whether it be USB2, Firewire or even wifi. Then again, I use
mostly laptops. I can get 50% saturation on my wifi link between a pair
of computers, and 25% using the ethernet link.

 

[R. C. White]

Hi, Ken.

I'd like to add a 4th factor affecting the speed of a backup:

4. How your files are organized. One giant file might be
read/written/verified quickly. But a million small files will take much
longer, because, in addition to writing the data itself, each file's name
and address must be written into the destination directory/folder. And if
they are in thousands of folders that must be created at the destination,
that will complicate matters and significantly increase the time required.

And one more thought: Can the backup be properly RESTORED to your computer?
Many users - my hand is up :>( - have found that their precious backup that
gives them such a comfy feeling is worthless because, for whatever
unpredicted reason - their Restore utility will not work with their backed
up data.

RC
--
R. C. White, CPA
San Marcos, TX
(e-mail address removed)
Microsoft Windows MVP (2002-2010)
Windows Live Mail 2012 (Build 16.4.3508.0205) in Win8 Pro


"Ken Blake" wrote in message

Basic question I know, but why does a back-up using Norton Ghost take
more than two hours? I thought computers carried out millions of
calculations every second. Is it to do with the writing time to the
back-up disc?

Calculation is not a significant factor. The time it takes is largely
dependent on three things:

1. How much you have to backup. This can vary enormously from one
computer to the next.

2. The speed of reading from the disk you are backing up.

3. The speed of writing to the backup disk (and note that if the
backup disk is external--as it should be--it's particularly slow).

But for most people, the speed of backing up is not very significant.
Start it before you go to bed at night and it should be done in the
morning. How long it took seldom matters.

 

[Ken Blake]

Hi, Ken.

I'd like to add a 4th factor affecting the speed of a backup:

4. How your files are organized. One giant file might be
read/written/verified quickly. But a million small files will take much
longer, because, in addition to writing the data itself, each file's name
and address must be written into the destination directory/folder. And if
they are in thousands of folders that must be created at the destination,
that will complicate matters and significantly increase the time required.

Yes, I agree--that's an important addition. Thanks.

 

[Ken Blake]

So in practical terms the speed of writing to the external disc is the
determinant?

The most important determinant is how much you are backing up (see
number 1, above). It takes about twice as long to back up 200GB as it
does to back up 100GB.

But if you want to talk about the computer, and you are backing up to
an external drive, what you say is correct (see the number 3 I
mentioned, above). External drives are much slower than internal
drives, so the speed of the drive you are backing up from is not very
important.

 

[Paul]

So in practical terms the speed of writing to the external disc is the
determinant?

On large numbers of small files, head movement is the determining factor.
While the head is moving on a hard drive, only the cache RAM is available
for (temporary) storage, and typically when you're between a "rock and a
hard place", the cache doesn't help (empty on read, full on write, no longer
helpful).

To stop that, try buying two SSD drives, one for the host machine,
one for the backup drive, and retest. How fast is it now ?
SSDs have seek times (when SATA connected), of around 100 microseconds.
At least 100 times faster than the hard drive.

Now, I've tested a few things here, on a RAM disk (4GB in size), and been
shocked and dismayed exactly how slow some operations are. Windows
search, searching for text, really isn't that fast. The only thing
that "screams", is computing a checksum on a large file stored
on the RAM disk. If you do anything involving the file explorer,
it's still dog-slow on a RAMDisk. So you'd be surprised how
software, with the "millions of calculations every second",
drags its ass. If I attempt to delete 60,000 files on the
RAM disk, it's like a slide show, when it should have been
a "flash of light" and "done". Makes no sense to me! The seek
time on a RAM disk (a real, hardware one in a box), is 1 microsecond
or less, and the RAM disk bandwidth (on my software one) is around 4GB/sec.
The poor performance could be due to the massive number of
context switches in the software stack, but that's just
a theory. The software in some of those paths, isn't exactly
tightly coupled. You may find, even when the hardware is
blazing fast (CPU and storage), the OS cannot process file system
calls faster than about one thousand of them, per second.

Paul

 

[Wolf K]

Why does the reading speed matter? Surely reading is faster than
writing and the computer can do both as the same time?

It's the HDD that reads and writes, and no, it can't do both at the same
time.

 

[J. P. Gilliver (John)]

In message <[email protected]>, Paul <[email protected]>
writes:
[]

Now, I've tested a few things here, on a RAM disk (4GB in size), and been
shocked and dismayed exactly how slow some operations are. Windows
search, searching for text, really isn't that fast. The only thing
that "screams", is computing a checksum on a large file stored
on the RAM disk. If you do anything involving the file explorer,
it's still dog-slow on a RAMDisk. So you'd be surprised how
software, with the "millions of calculations every second",
drags its ass. If I attempt to delete 60,000 files on the
RAM disk, it's like a slide show, when it should have been
a "flash of light" and "done". Makes no sense to me! The seek

I suspect at least some of that is the GUI, not the underlying OS. If it
has to redraw the Explorer window after each file deletion (or even each
windowful of such deletions), that will slow it down when doing that
many files. If it's possible (e. g. you're deleting all the files in a
single folder or similar), do it with the DEL command in a command
window, and see if that comes out any quicker.

time on a RAM disk (a real, hardware one in a box), is 1 microsecond
or less, and the RAM disk bandwidth (on my software one) is around 4GB/sec.
The poor performance could be due to the massive number of
context switches in the software stack, but that's just
a theory. The software in some of those paths, isn't exactly
tightly coupled. You may find, even when the hardware is
blazing fast (CPU and storage), the OS cannot process file system
calls faster than about one thousand of them, per second.

Paul

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

An Englishman, even if he is alone, forms an orderly queue of one. (George
Mikes
in "How to be an Alien".)

 

[J. P. Gilliver (John)]

On Sat, 03 Aug 2013 07:58:12 -0700, Ken Blake <[email protected]> []
Why does the reading speed matter? Surely reading is faster than
writing and the computer can do both as the same time?

It's the HDD that reads and writes, and no, it can't do both at the
same time.

Only if you're reading and writing from/to the same HDD, which isn't a
good backup policy, except at a secondary level.

 

[Gene E. Bloch]

Most of these image programs will only backup sectors in use and use
compression which probably adds some time.

In my experience, the time to compress the data is less than the time
saved by the smaller amount of data to write to my USB3 external drives.

Subjectively, in Macrium my time to create a new image is maybe half or
two thirds the time to create a clone. Note that Macrium only writes the
clusters that contain active data when cloning.

 

[Wolf K]

On Sat, 03 Aug 2013 07:58:12 -0700, Ken Blake <[email protected]> []
Why does the reading speed matter? Surely reading is faster than
writing and the computer can do both as the same time?

It's the HDD that reads and writes, and no, it can't do both at the
same time.

Only if you're reading and writing from/to the same HDD, which isn't a
good backup policy, except at a secondary level.

Well, yeah, but then one disk reads, and the other writes. Neither can
do both at the same time....

Have a good day.

 

[Gene E. Bloch]

On 2013-08-03 11:27 AM, Scott wrote:
On Sat, 03 Aug 2013 07:58:12 -0700, Ken Blake <[email protected]> []
Why does the reading speed matter? Surely reading is faster than
writing and the computer can do both as the same time?

It's the HDD that reads and writes, and no, it can't do both at the
same time.

Only if you're reading and writing from/to the same HDD, which isn't a
good backup policy, except at a secondary level.

Well, yeah, but then one disk reads, and the other writes. Neither can
do both at the same time....

Have a good day.

The real question is whether the controller(s) and the DMA (or whatever
passes for that in the 21st century: I'm pretty much 20th century
m'self) can do both at the same time, one process each on two separate
drives...

 

[Ken Blake]

On Sat, 03 Aug 2013 07:58:12 -0700, Ken Blake <[email protected]> []
Why does the reading speed matter? Surely reading is faster than
writing and the computer can do both as the same time?

It's the HDD that reads and writes, and no, it can't do both at the
same time.

Only if you're reading and writing from/to the same HDD, which isn't a
good backup policy, except at a secondary level.

I see my name up there in the attributions, but I didn't write
anything that you quoted.