FSCK at Boot – Importance with Journaled Filesystems

I was going to suggest hacking e2fsck to disable the specific checks for a last mount time or last write times in the future. These are defined in problem.c / problem.h, and used in super.c. But in looking, I discovered that E2fsprogs 1.41.10 adds a new option to /etc/e2fsck.conf called broken_system_clock. This seems to be exactly what you need, and since you're using Red Hat Enterprise Linux 6, you should have 1.41.12, which includes this option. From the man page:

   broken_system_clock
          The e2fsck(8) program has some hueristics that assume  that  the
          system clock is correct.  In addition, many system programs make
          similar assumptions.  For example, the UUID library  depends  on
          time  not going backwards in order for it to be able to make its
          guarantees about issuing universally unique ID’s.  Systems  with
          broken  system clocks, are well, broken.  However, broken system
          clocks, particularly in embedded systems, do exist.  E2fsck will
          attempt  to  use  hueristics to determine if the time can no tbe
          trusted; and to skip time-based checks if this is true.  If this
          boolean  is set to true, then e2fsck will always assume that the
          system clock can not be trusted.

Yes, the man page can't spell "heuristics". Oops. But presumably the code works anyway. :)

Fsck returns your filesystem to a consistent state. This is not necessarily the filesystem's “latest” state, because that state might have been lost in the crash. In fact, if there were half-written files at the time of the crash, then the filesystem was not left in a consistent state, and that is precisely what fsck is designed to repair. In other words, after running fsck, your filesystem is as up-to-date as it can get.

If your application requires feedback as to what is stored on the disk in case of a crash, you'll need to do more work than just writing to a file. You need to call sync, or better fsync, after a write operation to ensure that that particular write has been committed to the disk (but if you end up doing this a lot, your performance will drop down, and you'll want to switch to a database engine). You'll need a journaled filesystem configured for maximum crash survival (as opposed to maximum speed).

The property that an operation (such as a disk write) that has been performed cannot be undone (even in the event of a system crash) is called durability. It's one of the four fundamental properties of databases (ACID). If you need that property, read up on transactions.

Although filesystems are a kind of database, they're usually not designed to do well with respect to ACID properties: they have more emphasis on flexibility. You'll get better durability from a dedicated database engine. Then consider what happens in case your disk, and not your system crashes: for high durability, you also need replication.