Readynas 104 drops out when copying to it

evan, this sounds like metadata block size issues, that btrfs added in more recent kernels than the ReadyNAS OS uses to date (3.0 versus 3.4). Is this what 6.1.5 will contain? And if so, like Sparc, that block size change would require a factory default/new volume creation to take advantage of?

Allow metadata blocks larger than the page size (4K). This allows metadata blocks up to 64KB in size. In practice 16K and 32K seem to work best. For workloads with lots of metadata, this cuts down the size of the extent allocation tree dramatically and fragments much less.

Btrfs: Metadata blocks bigger than 4KB Btrfs was designed from the start to support blocks of multiple sizes, but the code wasn't ready and was disabled, so the Btrfs filesystems used as block size the size of a memory page (4KB in x86). In this version, support for metadata blocks bigger than a page size has been re-enabled, so Btrfs can use metadata blocks of up to 64KB in size (16/32KB seem to work better and are recommended). Support is enabled at mkfs time (f.e. mkfs.btrfs -l 32K). These block sizes cut down the size of the extent allocation tree dramatically and fragments much less. Can I change metadata block size without recreating the filesytem? No, the value passed to mkfs.btrfs -n SIZE cannot be changed once the filesystem is created. A backup/restore is needed. Note, that this will likely never be implemented because it would require major updates to the core functionality.