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What seperates zsplit/unzsplit from dd + gzip + netcat?

 
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Kakakoka
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PostPosted: Thu Apr 14, 2005 11:34 am    Post subject: What seperates zsplit/unzsplit from dd + gzip + netcat? Reply with quote

Hi,

A few days ago I found a page where it was demonstrated how to use dd, gzip and netcat to make/restore an hard drive image. I am wondering what does the zsplit solution offer that these simple tools does not?

Regards,
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jurij
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Joined: 05 Apr 2005
Posts: 54
Location: Germany

PostPosted: Thu Apr 14, 2005 4:59 pm    Post subject: Reply with quote

Hi Kakakoka,

Of course you have plenty possibilities using linux/UNIX such as dd, gzip and netcat to reach the
same or nearly the same result as with zsplit/unzsplit.
But what differs zsplit/unzsplit from these tools is following:

1. zsplit/unzsplit can deal with Very Large Files. gzip and bzip2 were not helpful for me to files bigger then 4 Gigabyte - with zsplit/unzsplit on the same machine, same kernel I can effectively treat files/devices as big as 200 Gigabyte and for sure even bigger.

2. With zsplit/unzsplit you have better software control over the process of compressing and splitting.

3. zsplit/unzsplit, comparing to tools mentioned above, can faster perform in compressing, because they use the compressing-in-memory algorithm from zlib library.

4. zsplit/unzsplit controll the creation, collection and glue together the splitted chunks.

5. One tool which combines features of different tools is easier to use in scripts as the combination of tools.

Regards,
Jurij
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Danno
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PostPosted: Thu May 05, 2005 11:23 pm    Post subject: What about speed Reply with quote

At this site,

http://www.rajeevnet.com/hacks_hints/os_clone/os_cloning.html

it says that just using dd to do an image, a typical 36g drive should only take about 50min to image over a 100Mbps link. I'm doing a 60 gig drive, I'm using zsplit and i'm at 4hrs and counting. Is this to be expected?

Also, is there a way to see how much time has elapsed or is remaining? The release notes says that there is better information now for these things. Where do I access it?

Thanks,

Daniel
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jurij
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Joined: 05 Apr 2005
Posts: 54
Location: Germany

PostPosted: Fri May 06, 2005 10:41 pm    Post subject: Reply with quote

Hi Daniel,

The imaging speed depends on many factors. Just some of very important among them: CPU speed, interface (IDE/ATA, SCSI, SATA which have very different transfer rates), hard drive buffer cache, the compression level and last but not least, there is a difference between local imaging and imaging over the network. So as you can see it is impossible generally to say that imaging from one device to other one using dd and netcat needs some definite amount of time in all cases and combinations of parameters mentioned above.
I think the time for imaging mentioned in the link is only very approximate value, which differs in one or other direction dependent on the hardware you are using and of course on the imaging tool .

For some comparing of the imaging speed which could be reached by zsplit, here some results of my tests:
Machine: Processor: GenuineIntel, Pentium4, 3.00GHz, Memory 1 GB, Devices: ATA/IDE Maxtor 200GB.
Imaging locally of 20GB device with test installation of WindowsXP.

Using dd+gzip compression level -9 : time 182 minutes
Using zsplit compression level -9 : time 185 minutes

So as you can see the speed of your imaging setup is comparable and not unusual.
I am now in preparation of the next release of zsplit/unzsplit. One of important improvements in this release is the tuning of both tools to reach the max possible imaging speed and compression rate.

Regards,
Jurij
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