A physical write error has occurred on the tar(1) output file, which is usually a tape, although it could be a diskette or disk file. Look on the system console, where the device driver should provide the actual error condition. The condition might be a write-protected tape, a physical I/O error, an end-of-tape condition, or a file-too-large limitation.
In the case of write-protected tapes, enable the write switch. For physical I/O errors, replace the tape with a new one. For end-of-tape conditions, try using a higher density, if the device supports one, or use cpio(1) or pax(1) for their multi-volume support. When encountering the file-too-large limitations, use the parent shell's limit(1) or ulimit(1) facility to increase the maximum file size.
For more information on tar tapes, see the section on copying UFS files in the System Administration Guide, Volume 1.