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G4L G4U (Read 7708 times)
Rad
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G4L G4U
May 6th, 2011 at 9:50pm
 
Received this email today. Perhaps some of you might find it interesting.

Quote:
I just released a new version of g4l (0.37), and generally to a search with date options to see what new has popped up. Your site popped up as it has in the past, and I looked around it. Lot of good info.

Some of the comparisons were not exactly correct.
Comparing a ghost image to a disk image is not the same, since normally a ghost image only backs up the files that are on a system, whereas a clone backups up all sectors used of not. Ghosts ability to resize images on the fly was great, but it did require it to be a supported OS.

Also, Ghost could do backups of linux when it was using older filesystems, but it failed with LVM, and that required a binary backup to be done. That is why I original looked at options, and found g4u, and later g4l.

Just wanted to drop a note. G4L is still free, and generally is setup to run from a cd, but can be transferred to usb or pxe relatively easy. I've even made a file that contains the lastest kernel and ramdisk.lzma file that can be booted using grub4dos from an ntfs partition using widows.

Thanks.

+----------------------------------------------------------+

  Michael D. S. II -  Computer Science Instructor      
  Guam Community College  Computer Center
  Guam - Where America's Day Begins                        
  G4L Disk Imaging Project maintainer
  http://sourceforge.net/projects/g4l/


I have been to Guam myself - twice. It's even closer to the equator than Hawaii, which is 22-degrees north latiture. Guam is 13, I think. Very humid.
 
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NightOwl
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Re: G4L G4U
Reply #1 - May 11th, 2011 at 9:47am
 
@
Rad

Quote:
Comparing a ghost image to a disk image is not the same, since normally a ghost image only backs up the files that are on a system, whereas a clone backups up all sectors used of (sic--I think he meant *or*) not.

Somewhat of a *purest* attitude--only a *sector-by-sector* image is a *disk image* and considered a *clone*! 

Using an appropriate switch, you can force Ghost to do a *sector-by-sector* image--but, the image file size will be much larger--approaching the size of the source HDD (or partition--if only a partition image is being made) minus any compression that might be used.  Ghost, if it recognizes the file system in use, will modify the backup so as to leave out *unnecessary* files (like the *Swap File* or the *Hibernation File*, plus it leaves out any *unused* sectors--but, if Ghost does not recognize the OS and/or the file system, it then switches to a *sector-by-sector* backup image.

Quote:
Also, Ghost could do backups of linux when it was using older filesystems, but it failed with LVM, and that required a binary backup to be done. That is why I original looked at options, and found g4u, and later g4l.

As I said above, Ghost can be configured to do a *sector-by-sector* backup if it is needed.  Ghost must have thought it *recognized* the file system--so, if it *failed*, it was because the file system had been changed so Ghost was mistaken.  So, *switching* to a *sector-by-sector* image should have solved that issue.

Quote:
found g4u, and later g4l

g4u = ghosting for unix

g4l = ghost for linux

So, there's *ghost*--the Symantec product, and then there's the other *ghost* products!  I guess one has to be careful how one uses the *ghost* name to mean what product, how it functions, and what type of image it creates!

Not trying to *dis* g4l--I hear it's a good product--just pointing out some comparisons.

 

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Dan Goodell
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Re: G4L G4U
Reply #2 - May 11th, 2011 at 6:32pm
 
Quote:
Ghosts ability to resize images on the fly was great, but it did require it to be a supported OS.

This kind of inaccuracy has always been a pet peeve of mine.  No, it does not require it to be a supported *OS*, it requires it to be a supported *file system*.  (Frequent readers of these forums may recall my similar frustration with those who would refer to Microsoft's MB-aligned partition layout as "Vista partitions".)


Quote:
Comparing a ghost image to a disk image is not the same, since normally a ghost image [does this] whereas a clone [does that].

Huh??  A legitimate argument would be: "Comparing a ghost image to a clone . . .", or else: ". . . a ghost image [does this] whereas a disk image [does that]".


Note I am not disputing the quality of the linux programs themselves, but the argument being put forth.  Arguments with technical or logical inconsistencies leave open the question of whether the one making the argument misunderstands concepts, or merely misspoke.

 
 
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Michael Setzer II
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Re: G4L G4U
Reply #3 - May 12th, 2011 at 6:20pm
 
I was commenting on a comparison of the speed of using ghost to other programs. To someone that didn't know anything about the processes used would simple take the difference in time to say the one program was just faster without truly understanding what is going on.

With g4l doing a raw disk image of an 80GB disk would take about 50 minutes, whereas a file level backup using the ntfsclone option on the same disk would take about 10 minutes with the space used. In both cases, the image sizes was very close in size.

My College had a site license for ghost, and contact them when the issue of LVM support came up, and just got a reply that it was not supported and wasn't going to be.

Ghost is an excellent product that meets the needs of many, and it does things that others don't do as easily.

reminds me of an old Car ad where they had there car getting 180 mpg, but it was a highly modified care under specific conditions.

Didn't mean to start anything, or say that my definition of the words were 100%.

Again, Thanks for the messages.
 
 
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NightOwl
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Re: G4L G4U
Reply #4 - May 13th, 2011 at 10:01am
 
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Michael Setzer II

Welcome to Radified Forums!

Quote:
Didn't mean to start anything, or say that my definition of the words were 100%.

Oh, please do *start things*--that's how we get into interesting discussions on the forums here!

Quote:
With g4l doing a raw disk image of an 80GB disk would take about 50 minutes, whereas a file level backup using the ntfsclone option on the same disk would take about 10 minutes with the space used. In both cases, the image sizes was very close in size.

Interesting--is that because *compression* reduces the size because the space is *empty* in unused sectors--and it can be compacted to a greater extent?

I guess even a *sector-by-sector* backup is not a *true clone* if it's a compress image file--the data has been *altered* by the image creation process and compression of data.  Yes, it all comes back when the image data is restored, but none the less it's not an *exact* duplicate--never thought about that issue before......I wonder if Ghost's *sector-by-sector* image file creation has the option to use *compression*--and if the file size will be similar to the *default* image file size where is *leaves out* unused space--I know the Ghost file will leave out known files that are unnecessary like mentioned above--i.e. swap file, hibernation file, etc.--when used in it's default image creation mode.

Quote:
My College had a site license for ghost, and contact them when the issue of LVM support came up, and just got a reply that it was not supported and wasn't going to be.

I was just trying to point out that there may be *workarounds* to what may otherwise appear to be a *failure* of the Ghost program.

Depending on how you ask the question, Symantec support may not be very helpful in their answers!
 

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Dan Goodell
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Re: G4L G4U
Reply #5 - May 14th, 2011 at 3:22am
 
    re: "In both cases, the image sizes was very close in size."

    NightOwl wrote:  "Interesting--is that because *compression* reduces the size because the space is *empty* in unused sectors--and it can be compacted to a greater extent?"
Yes.  That gets into the underlying compression algorithm--probably one of the ubiquitous derivatives of the granddaddy, Lempel-Ziv's encoding work.  It's a kind of shorthand.  For example, imagine representing a sector by writing "512x0" instead of writing down 512 discrete zeros on a piece of paper.  They both mean the same thing, but one is a lot shorter to write.

Even if the "empty" sectors are not entirely filled with zeros, if they are mostly the same or LZ can find lots of repeating patterns, it can be reduced to a relatively small shorthand equivalent.  The amount of compression that can be achieved is related to the amount of repeating patterns in the content.


Of course, Michael neglected to mention how much *data* was on his test disk . . .
    "With g4l doing a raw disk image of an 80GB disk would take about 50 minutes, whereas a file level backup using the ntfsclone option on the same disk would take about 10 minutes with the space used."
If you're only going to backup files, the proportion of time saved by a file level backup should theoretically be related to the proportion of the disk occupied by files.  It's not that one way compresses faster than the other way, it's just that one way ignores part of the disk.  If that disk contained 80GB of *data* then I think it should take about the same amount of time, either way. 


    NightOwl wrote:  "I guess even a *sector-by-sector* backup is not a *true clone* if it's a compress image file--the data has been *altered* by the image creation process and compression of data.
No, it shouldn't be.  You should be able to restore the exact contents of each original sector.

Keep in mind there are various strategies of what to include in the image.  It's a lossless compression algorithm, so whatever is included should be able to be restored precisely.  The question is what you're going to include.

In a standard Ghost image, as well as most Windows-based imagers, only the files are included--the used data area.  (And even then, they'll exclude files they consider non-essential, such as the pagefile.)  Those files can be reconstructed precisely, but as for the exact sectors they originally occupied . . . well, that info wasn't captured, so the restored files can't be put back exactly where they came from.  Hence, the familiar side-effect of restored images becoming "defragged" in the process.

A little more conservative approach is to capture both the files and where they came from, though still ignoring free space.  The old PowerQuest Drive Image used that strategy.  (IIRC, I think BING also does that.)  Thus, fragmented files would still be fragmented when restored.  However, anything that was in the original free space (such as deleted files) would not be restored because it wasn't captured.

Finally, a "sector-by-sector" or forensic image would also capture the contents of free space.  It can be compressed in an image without loss.  When restored, you not only restore the files to their exact locations, you also restore the contents of free space.  FWIW, I believe this is a practice used by law enforcement all the time--they make a forensic copy of the disk so they can work with the copy without damaging the evidence (the original disk), but still be able to unerase the bad guy's deleted porn files.

 
 
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Re: G4L G4U
Reply #6 - May 14th, 2011 at 3:49am
 
Quote:
Didn't mean to start anything, or say that my definition of the words were 100%.


It’s not my intention to flame or dismiss the contributions of others, if that’s the way it sounded.  My concern is not so much with imprecise language as it is with *misleading* language.

From the SourceForge page I see Michael is the project admin, so I think it’s pretty clear he *does* know the difference between a file system and an operating system.  But for other contributors, their backgrounds aren’t always clear.  When an incorrect statement shows up in a post, we can’t let it just stand, lest other readers take it as fact because nobody disputed it.  But did the writer just misuse a word?  Or is he spreading false information?

Without some context or background for the one making the statement, it’s often difficult to know.  Whereas Michael may have simply chosen the wrong word, somebody else making the same statement could be way off base and totally misunderstand the underlying principles they’re promulgating.

Some will dismiss this as mere semantics; I disagree.  A lot of well-meaning people have been led to false conclusions from something said incorrectly in some forum, and then gone around spreading that wrong information elsewhere.  I think it’s absolutely crucial for the integrity of a technical forum such as this to correctly present information that others may draw from.  It’s what makes the information on this forum so much more dependable than other tech sites—such as, say, forum.notebookreview.com, to use just one example.

An operating system and a file system are two very different things, but many people—especially newcomers—may not understand the distinction.  Yet understanding the distinction is critical if readers are going to be getting under the hood and comparing what these programs are doing.

If I sound dogmatic, it comes from over a decade of having to re-argue the same points over and over again.  For instance, I repeatedly hear from people who vociferously insist Ghost 2003 cannot work with Vista or Partition Magic can’t be used if you have Win7.  Such blanket statements are not technically true.

Yes, there may be some additional limitations when used with the latest OS’s, but that doesn’t mean they won’t work at all.  “Not completely compatible” is not the same as “incompatible”.  I can use Ghost 2003 to image and restore my Win7 OS partition, for example.  It’s all about understanding what it can do and what it can’t do.

To help others learn to know better, it's incumbent upon those of us who do know better to not mislead them.

As for G4L . . . to borrow a phrase Brian might use, I say "good on 'ya!"  I'm all in favor of broadening the arsenal of good tools we can all use.


 
 
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