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August 2008
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2008.08.22 15:21 "Re: creating sparse files......", by Toby Thain
On 22-Aug-08, at 11:44 AM, Bob Friesenhahn wrote: > On Fri, 22 Aug 2008, Rogier Wolff wrote: >> >> I'm stitching kind of large panoramas. This results in big >> intermediate files. On my last run, which took overnight to stitch, >> I thought 42 Gb of free disk space would be enough. Wrong! >> >> I got over thrity files of over 1.2Gbytes, filling up the disk. >> >> It turns out that most of the files contain lots of zeroes. On Unix >> this can be stored effciently by not issueing a "write" with a buffer >> full of zeroes, but by seeking over the area. The operating system >> will act as if the area was filled with zeroes. > > This is an interesting issue. While holey files seem like a > panacea, there can be some drawbacks. They are best for files > which are written just once (like core files) and not so good for > files which are expected to be updated in place. For files which > are updated in place, the updated hole is quite likely to increase > disk fragmentation since now it takes more space and the space will > need to be from some other place on disk. Fragmentation behavior > is quite filesystem dependent. > > It is worth considering enabling filesystem compression, or using > whole-file compression. Perhaps even just enabling normal TIFF > compression (e.g. LZW) is sufficient to eliminate the long spans of > zeros. Agreed, LZW (or even RLE) will be effective here. --Toby > > Bob > ====================================== > Bob Friesenhahn > bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/ > bfriesen/ > GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ > > _______________________________________________ > Tiff mailing list: Tiff@lists.maptools.org > http://lists.maptools.org/mailman/listinfo/tiff > http://www.remotesensing.org/libtiff/