Text File

Aucbvax.4912 fa.unix-wizards utzoo!decvax!ucbvax!unix-wizards Mon Nov 2 12:33:39 1981 Long tape records >From ARPAVAX.ghg@Berkeley Mon Nov 2 12:18:03 1981 Purdue/EE School uses 100 block (51200 byte) tape records for disk full dumps (epoch). The Unix "dump" program is not used for the full dumps. "Dbuf", a locally written program similar to "dd" in syntax, is used to make an image copy of disk filesystems on tape. Dbuf forks into 4 processes, one reads, one writes, one sends signals, and one is a watchdog. The read and write processes swap roles on alternating records, thereby providing the effect of double-buffered I/O. Our tape drive and disk transfer rates are about the same, so the time required for a copy is roughly equivalent to the hardware transfer rate (both are transferring at same time). Tape drive is a Telex 6253, 800/1600/6250 BPI @125 in/sec on an AVIV Unibus controller. Disks are CDC 9766's on System Industries 9400 SBI controllers (looks like DEC MBA to software). A 65500 block (512-bytes/block) filesystem can be dumped in 1-1/4 mins. Five 65500 block filesystems will fit on one 2400' reel of tape. System is a VAX 11/780 (dual cpu) running Berkeley 4.1BSD UNIX. Incremental dumps are still made via dump 6 days/week, and the full dumps are done on Sun morn. Both the disk and tape systems are pretty much rock solid (tape sys costs approx $30K). We use Graham Magnetics tape (Verituf or Epoch 480) which are suppose to have 1 and 3 Million pass lives. Dbuf is also almost twice as fast as dd for disk-disk xfers (on different controllers or MBAs) and the same speed as dd for the same controller or UBA. copies

There are no major problems with devices getting locked out for the long transfers, the SI disk controllers have a 4 sector buffer and the tape controller has a 4Kbyte FIFO for Unibus latency. There are even 3 1MBaud DMC-11's on the same Unibus which continue to function, although a little degraded. SI disks don't data-late like DEC ones do, they just miss revs. For this scheme to work there can be no badspots on the disk. One must either have good packs (we use Dysan) or use the Auto-badblock-forwarding in 4.1BSD to make them invisible.

Geo. Goble --ghg (ucbvax!pur-ee!ghg or CSVAX.ghg@Berkeley)

----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen <jgoerzen@complete.org> of http://communication.ucsd.edu/A-News/

This Usenet Oldnews Archive article may be copied and distributed freely, provided:

1. There is no money collected for the text(s) of the articles.

2. The following notice remains appended to each copy:

The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.