vinayak hegde posted on Thu, 01 Mar 2018 14:56:46 +0530 as excerpted: > This will happen over and over again until we have completely > overwritten the original extent, at which point your space usage will go > back down to ~302g.We split big extents with cow, so unless you've got > lots of space to spare or are going to use nodatacow you should probably > not pre-allocate virt images
Indeed. Preallocation with COW doesn't make the sense it does on an overwrite-in-place filesystem. Either nocow it and take the penalties that brings[1], or configure your app not to preallocate in the first place[2]. --- [1] On btrfs, nocow implies no checksumming or transparent compression, either. Also, the nocow attribute needs to be set on the empty file, with the easiest way to do that being to set it on the parent directory before file creation, so it's inherited by any newly created files/ subdirs within it. [2] Many apps that preallocate by default have an option to turn preallocation off. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
