On Wed, Feb 2, 2011 at 12:07 PM, Douglas Gilbert <dgilbert@xxxxxxxxxxxx> wrote: > There are a lot of zeros out there. Efficient use of sparseness > involves techniques to detect large quantities of zeros in > advance rather than just reading them all. And on the write side > there are standard techniques to append zeros to a file without > actually writing them. > > Seems a damn shame to read a terabyte of zeros and then write them > to another device or file. Carrying the idea further: if we know > random data has no meaning *** and we are asked to copy it, > why not "write" zeros to the output file? > > Over the last few years various commands have been added to the > SCSI and ATA command sets to better handle sparseness (and > trim/unmap/write_same can be viewed in this light). File systems > are improving their sparseness handling as well, with Linux > playing "catch up" to NTFS in this regard (e.g. the new > FALLOC_FL_PUNCH_HOLE flag in fallocate() ). > > So I am proposing a discussion of the: > - existing SCSI commands to support sparseness > - existing ATA commands to support sparseness > - suggestions for more sparseness support to be > added to the SCSI and ATA command sets > - user space tools that support sparseness > - file system support for sparseness > > Perhaps the latter point should involve the file system track as > well. Why not just acknowledge that arrays have some sort of allocation map and ask for a T10/SCSI command to return it. -- Regards, Richard Sharpe -- 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
