Linux – How to get checksum data integrity on ext4

I'm unaware of a filesystem-level checksumming; you could script (or hand-craft) using md5sum and store it in a text file for comparison, and there are ports of md5sum for multiple platforms.

If these are large files, you could consider setting up a system that lets users duplicate data using bittorrent; it has a built-in way of checksumming data and if you have several places that store the files you gain added benefits from not loading down one or two systems with transfers.

You might want to consider changing a policy on how the data is being duplicated or moved around if you're managing the systems or data; this would probably result in you losing less hair if something were to go wrong, and your users may thank you if something happens and "this time" the data wasn't backed up by Bob down the hall. You don't need to do anything too elaborate if you're working in an existing infrastructure; even a couple servers running a periodic rsync over the network (which would also be relatively fast since it transfers only changes in large files when transferring over networks, not so much if it thinks it's a local file) will create synced files.

I would caution that duplicating files like that and using checksums isn't technically a backup; it's a duplicate. Backups means that when your master file is corrupt you can "roll back" to a previous version (wanna set up something similar to CVS to check out your large data files?...) while duplicating, even with checksums, means that if your original is corrupted (accidental deletion, bad sector in the drive, etc.) that corruption will get copied out, checksum and all, to your duplicates, rendering them useless. You'll want to plan for that scenario.

I've worked in building a system for automation on boats, and there was a prerequisite: in every moment the power could go down and everything must boostrap again correctly.

My solution was to build a Gentoo-based initramfs system, with only a rw folder for application and configurations (this is the approach used by every router/firewall vendors). This solution add an additional layer of complexity when dealing with system upgrades, but assure you that the system will ALWAYS boot.

Regarding your specific question, you should keep EXT4 journal enabled for having faster fsck (of a few secods), use the data=journal mount option, lower the commit option or use sync option to keep buffers always empty.

Refs: http://www.kernel.org/doc/Documentation/filesystems/ext4.txt