On Sun, 2009-08-16 at 12:59 -0400, Christoph Hellwig wrote: > On Sun, Aug 16, 2009 at 10:52:07AM -0500, James Bottomley wrote: > > However, the enterprise has been doing UNMAP for a while, so we can draw > > inferences from them since the SSD FTL will operate similarly. For > > them, UNMAP is the same cost in terms of time regardless of the number > > of extents. The reason is that it's moving the blocks from the global > > in use list to the global free list. Part of the problem is that this > > involves locking and quiescing, so UNMAP ends up being quite expensive > > to the array but constant in terms of cost (hence they want as few > > unmaps for as many sectors as possible). > > How are they doing the unmaps? Using something similar to Mark's wiper > script and using SG_IO? Because right now we do not actually implement > UNMAP support in the kernel. I'd really love to test the XFS batched > discard support with a real UNMAP implementation. You mean how is the array vendor testing their implementation? Using SG_IO ... without any filesystem, I believe. The testing was initially done to see if the initial maximal discard proposal from LSF09 was a viable approach (which it wasn't given the time taken to UNMAP). James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
