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

[Jeff Garzik]

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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