I hope the following explanation goes some way toward answering your question. I also hope that it's not so horribly boring that old hands at this ask me why I am restating what some folks think we all should know in our sleep. The short answer is, yes, you can run the output from dd through a compresser like gzip (GNU ZIP). The long answer is, depending on what and how much you've backed up into the original image file, the compressed file may not be that much smaller. Archives and compressed multimedia files like MP3 are famous for not getting that much out of being re-compressed, so if you're backing up a partition that has lots of those kinds of files, you won't get that much compression, if any at all. OTOH, if your partition contains large portions of unused space, if that space contains nulls (or any other repeating character) the compression could be quite high and good. The problem is, if your partition has ever gotten full and then you cleaned up, you do know that your old files' data is still there, you've just lost the pointers to it, so because we're talking about an image backup here, not a file backup, the compressed image size could be adversely affected. This is where the trade-off between speed and efficiency comes into play. I could make a file backup that could conceivably be quite small compared to the actual partition size in which the source files originally resided, then make another kind of backup that would simply copy the rules of the partition mapping--how many tracks, cylinders, sectors, whatever, are in each partition and where each partition on the physical disk begins, that kind of thing is minuscule in size. In real life, though, we don't do that, we just launch a program that will create the partition we want to the size spec we want and then we restore the files. The problem with this approach is efficiency. It takes far longer to write individual files than it does to just lay down a solid stream of data from one end of the partition to the other because for every new file added to the partition, it takes two different kinds of disk accesses--one to query, then update, the master file allocation table and/or volume table of contents, and then another to actually go out there and lay down the restored files. Thankfully, though, improvements in hardware technology have brought this speed differential down to a manageable level. I distinctly remember years ago where full image backups on my DEC PDP-11 at work using 175-megabyte drives (RP06's for those who go back that far) took exactly 30 minutes, but a file backup after the disk was suitably prepared (read "initialized") could run all day. On Fri, 9 Jan 2009 13:55:01 -0600, you wrote:
Well, since linux reads the raw device as if it were a single file, it doesn't care what it is, it'd store it to a file and be able to put it back on the drive at a minimum. A talking live Ubuntu disk with Orca on should do this, but if you have 300 gig drives, will gzip compress out the empty space so you don't have to have a 300 gig image for a drive that may only have 40 or 50 gigs on it?
----- Original Message ----- From: "John G. Heim" <jheim@math.wisc.edu> To: <dave.mehler@gmail.com>; "Blind sysadmins list" <blind-sysadmins@lists.hodgsonfamily.org> Sent: Friday, January 09, 2009 9:43 AM Subject: Re: [Blind-sysadmins] Accessible Disk Imagers
I think you can image an ntfs disk with dd and gzip. I used to do that all the time with fat partitions. I haven't tried it with ntfs though. I kind of got out of the habit because linux didn't used to be able to write ntfs partitions. But it worked for fat16 partitions and now that linux can write ntfs, it would probably work for ntfs. The procedure used to be something like this:
1. Boot into linux. If you have a dual boot machine, great. Else use a live CD like oralux or grml. 2. Find enough disk space for the image, if you boot a live CD, you'll have to mount a network drive via nfs or samba. 3. Run dd with the in file being the fat or ntfs partition and out file piped to gzip.
The restore process is the same for steps 1 & 2 but the in file and out file are reversed for step 3.
I'll bet you can even make changes to the image by mounting it on a loopback device. I haven't tried it with ntfs but I've done it with fat16 many times. I'm about as sure as I can be that it would work because I've already mounted ntfs partitions and went in and deleted files.
----- Original Message ----- From: "Dave" <dave.mehler@gmail.com> To: "'Blind sysadmins list'" <blind-sysadmins@lists.hodgsonfamily.org> Sent: Friday, January 09, 2009 6:50 AM Subject: Re: [Blind-sysadmins] Accessible Disk Imagers
Hello, I'm also interested in this. For me another requirement would be to image several types of machines, Windows and Linux boxes for example. Thanks. Dave.
-----Original Message----- From: blind-sysadmins-bounces@lists.hodgsonfamily.org [mailto:blind-sysadmins-bounces@lists.hodgsonfamily.org] On Behalf Of Steve Matzura Sent: Friday, January 09, 2009 6:00 AM To: blind-sysadmin Subject: [Blind-sysadmins] Accessible Disk Imagers
I'm the sys admin for a small network--my home network--which has, among other things, five desktops and two laptops running XP SP2. I recently had to rebuild one after something, and I still don't know what that something was, turned most of my machine into just so much cole slaw. It all started with trying to uninstall a trial version of a voice dialer called VoiceIt or something similar. Anyway, the uninstall went bad, and took the rest of the machine with it.
One New Year's resolution I'm deciding is a must-keep is to image all my boot drives in the house and pack 'em away against the day, which will hopefully never come, when I need them. I just took a Dell Dimension 4700 and rolled it back to factory defaults through use of the Dell System Recovery Environment (DSRE), which is a fancy shmancy name for nothing more than a hidden partition with a Ghost image and some batch file control on the front end to automate the process. I had just a wee bit of trouble with it in that somehow something (possibly even the deinstall of VoiceIt) had broken the master boot record for the hidden partition wherein the DSRE is located. Thanks to a gentleman on the net named Dan Goodell, I was able to put Humpty Dumpty together again and with about two minutes help from my self-proclaimed Ludite wife, brought the 4700 back to life. This is Something I wish not to have to repeat. Ever.
What was great about the DSRE was that it worked flawlessly. What was horrible about it was, of course, that it had no speech. So now that the computer's been completely updated and all the software I want on it has been reinstalled and everything's at a nice stable state, it's now time to do the deed and make another image, this one hopefully bootable from a CD and maybe even with some speech and accessible. Mind you, I'm going to have to do this, whatever it is, at least six times, so I'd like whatever I build to be accessible everywhere. I was even thinking really big like get a USB drive and put all the images on it and have a bootable front-end where I select which image I want to restore, and it just goes and does it. What are folks thoughts on how to do this?
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