OT: Disk Image (ISO) storage vs. copy of disk

johnmeyer wrote on 10/14/2009, 8:44 AM

Does anybody know if there is an advantage to storing a disk (DVD or data) as a Disk Image (ISO) over just making a copy? Does an ISO provide error checking or checksums that verify the integrity of the ISO during creation and expansion?I can think of a lot of negatives to this approach. If a sector on the storage medium which holds the ISO image fails, it might be difficult to recover the files on the sectors which are still OK. By contrast, if you store the individual files, those still on the good sectors should copy without any further effort.

Depending on the file system, the ISO image might take less space because -- and I think this is correct, but I'm not sure -- there is no "slack" in an image file (the leftover space between the actual data in your file, and the fixed block size that your file system uses to save files). So, you get a little free "compression" with the ISO file.

As to whether there is extra error checking or checksums, I think you are talking about the kind of thing that happens on a DVD or CD, where the files are stored in such a way that if certain bits cannot be read because of faulty pits or scratches on the surface, those bits can be reconstructed from redundant information stored elsewhere on the disc. I don't know if that same information is stored in the ISO image or if it could be used to reconstruct the contents of the ISO image.

To me, the reason an ISO image exists is that it provides a single-file representation of a disc which can therefore be moved around simply. Also, when burning, the information can be more or less just copied from the ISO image. In the old days, when there weren't many buffers on drives, there were lots of burn failures ("buffer underruns") when trying to read thousands of really small files, and the disk drive couldn't find all the fragments in time to satisfy the requests from the burner drive. The ISO file solved that problem, so many people started creating ISO files and burning from that. With modern drives, this is seldom if ever needed.

I'm sure others know a lot more about this than I do and will have other things to add.

Former user wrote on 10/14/2009, 9:24 AM

John,

Thanks, you have provided some valuable information. I think you answered my main concern. I was curious if this was a more secure way to store the information.

Thanks,
Dave T2

DaveM2 wrote on 10/14/2009, 12:52 PM

For another point of view, although I am new to Vegas I have been creating DVDs for clients for many years. I like ISO's - and create all my DVD disks from iso's.

Once I have a master DVD from an iso - it goes in storage, as does a backup copy of the iso - which I copy to a DVD for storage and I generally keep a copy of the iso on a hard drive as well.

I have had master dvd's go bad (why I don't know - but it is a sinking feeling putting a master dvd in a drive to copy and having the copy program tell you "unable to read DVD " I have never had an iso. go bad, although I have lost hard drives before (thankfully not the drives I have dedicated to backups) - but that possibility is always there.

I don't think there is much difference in security between dvd vs iso, and burn programs have error checking in writing out to a dvd.

I started using ISO's more when I noticed I could make faster copies from ISO's than from a master dvd - which makes sense since the burn program doesn't have to read the master before makig the copy. And transfers of data are generally faster from a fixed disk than a dvd drive.

That's my 2 cents.

gpsmikey wrote on 10/14/2009, 7:11 PM

I second the ISO route - I keep an ISO on my hard drive which does get backed up. There are also a number of utilities out there to create MD5 or SHA etc "check sums" for files (your ISO in this case). This is typically how they distribute Linux distro's for example - you download the ISO of the install disk run the check against the published check value and you know you have a valid image to work with. An ISO image is also only as big as it needs to be - if your DVD only takes up 1 gig, then the ISO will be about that size also - it does not save the unused portions of the disk.

A bit OT (but not a lot) - there are a number of free utilities like Imgburn out there that can not only burn from an ISO, but create an ISO of an existing CD or DVD - makes a handy way to save a copy of that install CD for windows etc to your hard drive - you can then re-create the disk as an exact copy at any time (including if it is bootable).

mikey

johnmeyer wrote on 10/14/2009, 9:07 PM

At the risk of straying a little further off topic, but still on the subject of ISO files, since you mentioned Imgburn, does anyone know of a utility which can read the ISO files created by DVDA when creating a DVD-5 disc that can be played on a Blu-Ray player? I have created several of these, but am not sure what to use to burn them.

farss wrote on 10/14/2009, 10:31 PM

Just to get a bit back on topic.
My limited understanding is that replicators may prefer ISO because it is a bit for bit exact image of how the disk should be made. Give them a disk of files e.g. an authored DVD that they copy the files from and their master might not end up being a physical copy of your master. That said I've made a few masters that went out for replication and never once been asked for an ISO image. That may have been different if they were dual layer DVDs.

The other thing I'd throw into the mix is my concern regarding audio CDs. The error correction on them can leave a lot to be desired. By design it was designed to correct errors in a way that gave the least offensive auditory result. In other words the sound quality can degrade because of errors and you might not be aware of this. My policy is to backup audio as data files.

When it comes to media the MAM disks are the best but they are not cheap. The very best are medical grade CDs made by Kodak but at $10 per disk I've not tried these.

Bob.

Former user wrote on 10/15/2009, 5:49 AM

Mikey,

Do you have any programs that you suggest for creating checksum files for ISO?

And thanks to everybody for their input on this topic.

Dave T2

gpsmikey wrote on 10/15/2009, 8:00 AM

I haven't looked for a while, but one I have used is md5summer http://www.md5summer.org/ (runs under windoze, but is compatible with the Linux MD5Sum utility ). I had wanted a utility that added itself to the windows context menu (right click), but did not find one I liked at the time. There are more reliable "checks" such as the SHA etc, but for most people, the chances of something getting past the MD5 check are pretty small.

mikey

MarkWWWW wrote on 10/15/2009, 8:58 AM

As well as its image creating/burning features, ImgBurn will calculate the MD5 hash for the ISO.

Mark

Former user wrote on 10/15/2009, 10:35 AM

Mark,

So IMGBURN will create an MD5 log or whatever to check the integrity of the file? Is this a built in function or an addon?

Thanks,

Dave T2

Byron K wrote on 10/15/2009, 11:54 AM

Posted by: DaveT2, Date: 10/14/2009 5:21:56 AM
You may want to try the built in Windows ntbackup utility. I use it all the time to archive files and can port it to any machine that has ntbackup.exe or just carry ntbackup.exe on a thumb drive. It also has Normal, Differential, Incremental types of backup, you can also verify the data after the backup. You can also Append the current backup to an existing backup file or just replace the backup file.

Another thing is that you can extract specific files or folder w/ out having to extract the whole backup file to another folder and you can burn or archive this file as a regular data file.

The best part is that it's FREE. It's been part of Windows since NT and has been rock solid, at least for me.

The only thing is, the extraction process is a "little" convoluted, but not to difficult to figure out.

MarkWWW wrote on 10/15/2009, 1:04 PM

It's built-in.

Calculating the MD5 hashes needs to be turned on by ticking the appropriate box on Page 2 of the General tab in Settings. This will cause it to write the MD5s values to the log that it create as it works its way through the imaging or burning operation.

In addition, on the Read and Build tabs you can tick a box which will also write the MD5 hash to a text file that it puts in the same location as it puts the ISO file, so that you can keep it for comparison purposes later.

Mark

Former user wrote on 10/15/2009, 1:39 PM

Mark,

Thanks for the info. That is what I was interested in doing with my archive and ISO files.

Dave T2

Former user wrote on 10/15/2009, 1:40 PM

Byron,

I have never been real happy with BACKUP programs that windows provides. As you say, the extraction process is always painful.

Dave T2

Byron K wrote on 10/16/2009, 10:12 AM

Posted this on the "What do you recommend for backup software?" Thread.

Windows Backup Utility
File Recovery

Launch Windows Backup Utility, Click: “Restore Wizard (Advanced )” button,
At the Welcome to the Restore Wizard window, Click: Next

Click File “+” to expand the backup files and Select the Backup Files in “Items to restore” list it the Restore Wizard.

Click the “+” of the backup file to be restored and select the folders to restore. (Individual files can be restored at this point.) Click: Next.

At the “Completing the Restore Wizard” Screen, Click: Advanced

Select Restore files to an “Alternate Location”
Click: Browse and select a folder to restore the files. (It’s best practice to restore files to an alternate location than the original in the event the original location has physical disk errors.)

At the “How to Restore” screen select: “Replace existing files” and Click: Next.

At the “Advanced Restore Options” Verify the following are selected and Click: Next.
Select: Restore security settings
Select: Preserve existing volume mount points

At the “Completing the Restore Wizard” screen, Click: Finish

Soniclight wrote on 10/16/2009, 12:37 PM

I considered ISO for a while but ended up with using Acronis TrueImage. Many people at this community use it too. Very affordable, fast, hassle free, never had a problem restoring entire system. Beats Symantec Ghost by miles, IMO.

One can also just back up specific folders, etc. Has ability to create non-OS accessible Safe Zone on drive that only True-Image can access, like a stealth/secret section of drive (I haven't had the need for this last option but it's a good one).

Acronis TrueImage