HSM team, Reading this thread got me taking a basic look at ext4 for the first time. I get the impression from what I read that ext3 is basically feature frozen for new features and that major improvements like a HSM would need to go into ext4 if they are to be accepted into the kernel. Why are you working with ext2 / 3? Is it just a stepping stone to ext4? One specific ext4 only feature is support for SSD discard commands. SSDs function optimally when they know which sectors have valid user data in them. Therefore ext4 calls discard for data blocks that are part of deleted files. ext2/3 does not have an ongoing effort to do this and I don't know if anyone will add that functionality to it or not. FYI: the linux vfat and btrfs filesystems also have SSD discard functionality. I don't think the others have addressed this new optimization yet. Also ext4 has a online defrag capability. (I'm not positive if this feature is in 2.6.28 or not. I did not look, but as of 2.6.28 ext4 is "stable".) Since defrag has to move user blocks around in a live system with minimal impact on user space, I would think you could look at this code in ext4 and get another idea of how to do that, and if ext4 is your target, you might be able to leverage some of the defrag infrastructure. ie. Maybe just replace the data block allocation requests with your own. If you try to plug-in to the existing defrag logic, you may even be able to extend it in such a way that allows HSM to be a module. Being a module would be very cool. It would allow HSM to be used on distro kernels that don't want to have HSM in them officially. In particular the OpenSUSE kernels allow modules to be added that are not part of the official distribution. Greg -- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
