Re: Notes on support for multiple devices for a single filesystem

Jeff Garzik
2008-12-17T21:30:00Z

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