Andreas Dilger wrote:
I can't speak for btrfs, but I don't think multiple device access from
the filesystem is a "layering violation" as some people comment. It is
just a different type of layering. With ZFS there is a distinct layer
that is handling the allocation, redundancy, and transactions (SPA, DMU)
that is exporting an object interface, and the filesystem (ZPL, or future
versions of Lustre) is built on top of that object interface.
Furthermore... think about object-based storage filesystems. They will
need to directly issue SCSI commands to storage devices. Call it a
layering violation if you will, but you simply cannot even pretend that
an OSD is a linear block device for the purposes of our existing block
layer.
Jeff
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