I'm very excited about the new features of btrfs and would like to start tesing it.
Before I get started, I would like to ask if btrfs supports increasing raid capacity by replacing disks by bigger ones (and not adding additional disks).
Example:
A RAID10 consisting of 8x 2TB drives results in a capacity of 8 TB. Then, each 2TB drive gets replaced by a 6 TB drive. After each disk replacement, a rebuild / rebalance is executed. I'm wondering, if after the last disk replacement and rebalance the capacity jumps from 8TB to 24TB?
There is some lecture about it in the internet, but there is no 100% statement like "yes, after rebalance, the capacity gets increased!".
https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices#Adding_new_devices
The NAS devices from Synology support exactly the feature I'm asking about: https://www.synology.com/en-global/knowledgebase/DSM/help/DSM/StorageManager/volume_diskgroup_expand_replace_disk
But, I'm not sure, if this feature is a native feature of btrfs or if the developers from Synology created it especially for their disk station operating system.
Best Answer
Yes, the capacity will grow in btrfs when you replace the drives with bigger ones. But make sure you always have backups! While the RAID0/1 code is not nearly as buggy as the RAID5/6 code in btrfs (as of 07/2016), your device replacement would not be the first one to go horrible wrong.