Mount Rainier (packet writing)

Mount Rainier (MRW) is a format for writable optical discs which provides the packet writing and defect management. Its goal is the replacement of the floppy disk. It is named after Mount Rainier, a volcano near Seattle, Washington, United States.

Mount Rainier can be used only with drives that explicitly support it (a part of SCSI/MMC and can work over ATAPI), but works with standard CD-R, CD-RW, DVD+/-R and DVD+/-RW media.

The physical format of MRW disks is a layer placed in between the file system (e.g. UDF or FAT32) imposed by the operating system or the packet writing software used to write or read the disk and the physical layer which determines how data is written to or extracted from the optical disc. This is transparently managed internally by drive's firmware which remaps physical drive blocks into a virtual and defect-free space. Therefore, the host computer does not see the physical format of the disk, only a sequence of data blocks capable of holding any filesystem.

The time needed for the disk formatting is shortened to about one minute by the background formatting capabilities of the drive. Formatting allocates some sectors at the end of the disk for defect management. Defective sectors are recorded at a table in the lead-in (an administrative area) and in a copy of the table in the lead-out.

From the host computer's perspective, an MRW disc provides a defect-free block-accessible device, upon which any host supported filesystem may be written. Such filesystems may be FAT32, NTFS, etc., but the preferred format is usually UDF 1.02, as this file format is widely supported. An MRW-formatted CD-RW with a UDF filesystem gives approximately 500 MB free space.

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