Linux

Efficiently synchronize copies of a large sparse file locally. I deal with a large amount of large sparse files because of virtualization and other technologies. Because of their size, often a small number of blocks have data and, of these, a small number of blocks are changed and need to be backed up. Using a log-based (snapshotting) file system on USB 2 as a backup device, I only want to write blocks if absolutely necessary.

So what's the solution?  Some simple custom code that

1. checks that both file sizes are identical;
2. verifies that some metadata has changed (i.e time stamp, permissions or owner/group);
3. reads both files block-by-block;
4. writes only changed blocks to the destination file, and
5. updates any changed metadata.

This brief HOWTO shows how to take a working 32 bit 12.04 installation and convert it into a 64 bit system. You will be able to keep all your programs, settings and data. You start with a 32 bit system that can run 64 bit programs, then convert it to a 64 bit system that can run 32 bit programs.

With the upcoming release of Debian GNU/Linux wheezy, a new feature called multiarch is being introduced. The facility permits the installation of executable files (such as libraries and programs) from multiple architectures simultaneously on the same system. The primary use of this is to allow 32 bit programs to be run on a 64 bit system, but it has other uses.

With the release of Ubuntu LTS 12.04 (Precise Pangolin), this feature is available now.