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What folders in the root folder ( "/" ) cannot be moved to a clustered file system (using DRBD and probably GFS2)?

Would like to setup a basic cluster to increase uptime for our file server, web server, and database and would prefer to use a clustered file system for the host OS (Debian) as much as possible. Was wondering what folders cannot be moved to the clustered file system.

We currently boot from a RAID1 using GRUB and would keep those folders that cannot be moved on the RAID1 and then Rsync or something to keep the servers synced for just those folders. But would like to minimize what is Rsync'd and just keep as much as possible on the clustered file system.

If this sounds like a bad idea, would be curious as to why.

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You'll need /boot on local media, unless you netboot. Other than that, your initramfs just needs to get rootfs mounted—it doesn't matter where it comes from. So with enough tools added to the initramfs, you should be able to have / on DRBD.

Of course, some parts of / are not really supposed to be shared with other machines. At minimum, parts of /etc and (almost) all of /var and /run (note /run is often a tmpfs). To boot multiple machines off the same rootfs, you'd need to make those their own filesystems (or otherwise arrange each machine to have its own).

[I'm not sure how this is increasing your availability beyond having all the data on a shared filesystem.]

  • I can see how it would be prudent to keep the system logs, temp files, Host OS specific files and the likes on the local drive. This gives good logical direction. For some reason searching was not getting me anywhere. – Damon May 18 '15 at 18:43
  • I'll note also that package management becomes much more difficult if you share stuff between machines—the package manager state is in /var (probably not shared), and you have to figure out how to keep it in sync with what's really installed... – derobert May 18 '15 at 18:51
  • Server syncing seems to be a issue that plagues all admins. Seems like there should be a simple linux solution to this to create a master/slave OS. that handles everything above the hardware layer to keep things synced because software and configuration will be exactly the same except where required by hardware and network topology. – Damon May 18 '15 at 18:59

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