2/24/2023 0 Comments Convert image format dd to folders![]() ![]() sparse-fio - dd-like program to work with files that are sparsely filled with non-zero data.Resize_reiserfs: Resizing finished successfully.įilesystem Size Used Avail Use% Mounted on Resize_reiserfs 3.6.21 (2009 ReiserFS report: Next, we need to increase the size of its filesystem: This will increase its size to 1 Gb, and leave its information intact. Should you ever need to grow a file, you may do the following: $ echo "This is a test to see if it works." > folder/file1 Now, let us add some content to one of the files: $ find path/ -type f -printf '%S\t%p\n' | gawk '$1 < 1.0 done The above command can be easily extended to list sparse files in a desired path: $ find sparse-file.bin -printf '%S\t%p\n'Ī sparse file has a sparsiness value of less than one whereas normal files have exactly one or just slightly above. The same can be achieved with du by comparing:Ī step further is to print sparsiness value with find: If a file size is greater than the allocated size in the first column a file is sparse. ![]() This is not a bulletproof method if the filesystem uses compression, extended attributes take up the difference in space, file is internally fragmented, has indirect blocks, and similar. Since sparse files occupy less blocks than the apparent file size would require, they can be detected by comparing the two sizes. ![]() Note: Be sure to include the loop option, otherwise it will not mount. The following command creates a non-sparse copy of a (sparse) file: The fallocate utility can make existing files sparse on supported file systems: $ du -h -apparent-size file.img 512M file.imgĪnd, to check the actual size of a file on disk:Īs you can see, although the apparent size of the file is 512 MiB, its "actual" size is really zero-that's because due to the nature and beauty of sparse files, it will "expand" arbitrarily to minimize the space required to store its contents. To check a file's apparent size, just run: Sparse files have different apparent file sizes (the maximum size to which they may expand) and actual file sizes (how much space is allocated for data on disk). ![]() $ dd if=/dev/zero of=file.img bs=1 count=0 seek=512M The dd utility can also be used, for example: This command creates a 512 MiB sparse file: The truncate utility can create sparse files. The advantage of sparse files is that storage is only allocated when actually needed: disk space is saved, and large files can be created even if there is insufficient free space on the file system.ĭisadvantages are that sparse files may become fragmented file system free space reports may be misleading filling up file systems containing sparse files can have unexpected effects and copying a sparse file with a program that does not explicitly support them may copy the entire file, including the empty blocks which are not on explicitly stored on the disk, which wastes the benefits of the sparse property of a file. Sparse files are commonly used for disk images (not to be confused with sparse images), database snapshots, log files and in scientific applications. Most modern file systems support sparse files, including most Unix variants and NTFS, but notably not Apple's HFS . The application is unaware of this conversion. When reading sparse files, the file system transparently converts metadata representing empty blocks into "real" blocks filled with zero bytes at runtime. The full block size is written to disk as the actual size only when the block contains "real" (non-empty) data. This is achieved by writing brief information (metadata) representing the empty blocks to disk instead of the actual "empty" space which makes up the block, using less disk space. According to Wikipedia, in computer science, a sparse file is a type of computer file that attempts to use file system space more efficiently when blocks allocated to a file are mostly empty. ![]()
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