I am trying to build a server that will be my NAS/Media server as well a the XBMC front end. I am planning on using Ubuntu with btrfs for the NAS part of it. The current setup consists of 1TB hdd for the OS etc and two 2TB hdd's for data. I plan to have the 2TB hdd's used as JBOD btrfs system in which i can add hdd's as needed later, basically growing the filesystem online. They way I had setup the file system for testing was while installing the OS just have one of the HDD's connected and have btrfs on it mounted as /data. Later on add another hdd to this file system. When the second disk was added btrfs made as RAID 0, with metadata being RAID 1. However, this presents a problem: even if one of the disk fails I loose all my data (mostly media). Also most of the time the server will be running without doing any disk access, i.e. the HDD's can be spun down, when a access request comes in this with the current RAID 0 setup both disks will spin up. in case I manage a JBOD only the disk that has the file needs to be spun up. This should hopefully reduce the MTBF for each disk. So, is there a way in which I can have btrfs setup such that metadata is mirrored but data stays in a JBOD formation?
Another question I have is this, I understand that a full drive failure in JBOD will lose data on the drive, but having metadeta mirrored across all drives, will this help the filesytem correct errors that migh creep in (ex bit rot?) and is btrfs capable of doing this.
Best Answer
It would seem that your question is best answered here:
https://serverfault.com/a/438181/89037
Basically, yes, the "single" data profile allows disks of different sizes and combines them in JBOD fashion. Don't change the metadata, leave as RAID1.