A typical operating system requires a boot disk and certain storage requirements to reside, boot and do what it's designed to do. The OS or boot disk where the operating system resides in a conventional install becomes a possible point of failure. The OS disk failing, would cause an
outage and cut-off access to your data and storage appliance. RAID 1 or mirroring of the OS disk is often used to address/counter this type of failure. ZFS has the features to make an OS disk redundant by mirror-ing (RAID 1), providing an added layer of insurance to your storage appliance's uptime.
A design decision with EON, was to make it run from a RAM disk, hence it would not have an associated failure attached to the media(USB, CF or hard disk) it boots from or resides on. Size becomes a disadvantage running from a RAM disk but the trade off is an add layer of insurance, resilience and uptime. EON uses the boot/residence media mostly for out of band task that are not tied to performance and are not frequently used, so the typical 5+ MB/s performance of a USB/CF media is not a problem. After EON is booted, the USB media could be pulled (simulating a boot disk failure) and only the services below would be impacted. The important thing to note is that EON would continue to run, along with all the services enabled. The show goes on and facilitates dynamic repair or correction of the disk failure situation. EON uses the USB/CF media to preserve:
- edits to the configuration files
- edits to the grub menu entries or updating the image
- updates to the zpool.cache
- user optional binaries on the USB/CF media
A ZFS boot/root was recently requested as a necessary feature/requirement for EON. I explained the resilience already built into the design and the challenges. I however gave it try the other night and succeeded in booting EON on a ZFS boot/root. This would allow the use of redundant USB/CF media. When will it be seen in a release? I'm not sure. It required using steps that were hard coded and needs more testing and refinement before it's ready for general audience and use. So yes, a ZFS boot/root for EON is possible. Here's a ZFS boot/root birth cry screenshot.
