Power-Safe filesystem

The Power-Safe filesystem, supported by the fs-qnx6.so shared object, is a reliable disk filesystem that can withstand power failures without losing or corrupting data.

Its features include the following:

• 510-byte (UTF-8) filenames

  You can't use the characters 0x00-0x1F, 0x7F, and 0xFF in filenames. In addition, / (0x2F) is the pathname separator, and can't be in a filename component. You can use spaces, but you have to “quote” them on the command line; you also have to quote any wildcard characters that the shell supports. For more information, see “Quoting special characters” in Using the Command Line.

• copy-on-write (COW) updates that prevent the filesystem from becoming corrupted by a power failure while writing
• a snapshot that captures a consistent view of the filesystem

For information about the structure of this filesystem, see “Power-Safe filesystem” in the Filesystems chapter of the System Architecture guide.

To create a Power-Safe filesystem, use the mkqnx6fs utility. For example:

mkqnx6fs /dev/hd0t76

You can use the mkqnx6fs options to specify the logical blocksize, endian layout, number of logical blocks, maximum number of inodes (and hence, files), and so on.

Once you've formatted the filesystem, simply mount it. For example:

mount -t qnx6 /dev/hd0t76 /mnt/psfs

By default, the Power-Safe filesystem creates sparse files when growing a file with ftruncate() or when writing at an offset that is beyond the end of a file. The filesystem counts sparse blocks against the total free space, so it isn't possible to overcommit the disk blocks. To maintain compatibility with previous versions of the filesystem (i.e. versions prior to QNX Neutrino RTOS 7.1), use the nosparse mount option.

For more information about the options for the Power-Safe filesystem, see fs-qnx6.so in the Utilities Reference.

To check the filesystem for consistency (which you aren't likely to need to do), use chkqnx6fs.