What's the difference between "Block Copy" and "Installing" an OS?

[McAwesome]

I was helping another JSS install figure out why their imaging was taking 1h40m while ours was only taking 15m. Turns out the issue is that theirs was installing and ours was block copying. I let them know that was the issue, and they asked what the difference was. I had no answer other than that one was significantly faster. I tried looking it up online, but I can't find a satisfactory explanation of the difference.

What exactly is the difference between block copy and an install of an OS?

[Look · Accepted solution]

The fundamental diference is the source media.

If it says installing it is running the OS X installer that someone has dropped into Casper Admin.
If it says block copying it is simply copying an already installed OS X onto the volume i.e. something created with Autopkg or having images precompiled before deployment.

The first one queries the machine etc... and installs components and packages as it feels appropriate, the later simply makes an identicle copy of a large file.

[robintosh · Accepted solution]

Block copy is a "brainless" operation in which an image is restored, block y block, to a destination disk. The OS is unaware of the files, permissions, attributes, etc, etc. To perform a block copy the destination partition is erased.

An install goes file by file and can perform lots of logical operations in order to upgrade and keep files.

If you want to delete a system and restore to a known state, it's more convenient a block copy restore. If you want to upgrade or install a system without deleting the destination you must install.

Cheers!

Robinson

[Look · Accepted solution]

The fundamental diference is the source media.

If it says installing it is running the OS X installer that someone has dropped into Casper Admin.
If it says block copying it is simply copying an already installed OS X onto the volume i.e. something created with Autopkg or having images precompiled before deployment.

The first one queries the machine etc... and installs components and packages as it feels appropriate, the later simply makes an identicle copy of a large file.

[McAwesome]

@Look Interesting. Is there any real advantage to installing rather than block copying? We've been using the latter due to speed and haven't had any issues on a variety of machines. Is there something we're just unaware of that could bite us down the line?

[robintosh · Accepted solution]

Block copy is a "brainless" operation in which an image is restored, block y block, to a destination disk. The OS is unaware of the files, permissions, attributes, etc, etc. To perform a block copy the destination partition is erased.

An install goes file by file and can perform lots of logical operations in order to upgrade and keep files.

If you want to delete a system and restore to a known state, it's more convenient a block copy restore. If you want to upgrade or install a system without deleting the destination you must install.

Cheers!

Robinson

[Look]

@McAwesome you will as time goes on encounter the odd package that simply doens't like to be compiled.
Casper Imaging looks to be pretty clever though, if you have a configuration that contains both a prebuilt OS and additional packages, If you prioritise the OS so it install first it will actually block copy this and then regulary install any addtional packages.
Also if your using precompiled images (so it block copies the entire thing) then changing any individual package would mean that the compiled image was wrong meaning either Casper imaging couldn't use it, or if it did it would contain the wrong version of the package.
We have opted for prebuilt OS and then everything else as additional normal installs.
It makes the OS install part fast and reliable and also when we want to thin image we use the exact same configuration minus the OS dmg. But still leaves the system flexible and easily updatable. We were also having issues with installing OS X directly out of Casper on some hardware for some reason. This is our first year of using Casper Imaging (previously Deploy Studio) but it's looking pretty good.

[davidacland · Accepted solution]

The block copying is much faster because the computer won't have to apply any intelligence. As the other posters mentioned, it just copies block 1 on the source disk image to block 1 on the target drive and so on. Installing a package requires the computer to read files to determine where things need to get put.

It's also more efficient on traditional magnetic hard disks as the read and write operations are in a continuos stream.