pinard@odyssee.UUCP (Francois Pinard) (06/20/88)
In article <314@marob.MASA.COM>, samperi@marob.MASA.COM (Dominick Samperi) writes: > Where can one find the QIC-xx streaming tape standards documented? I would also like to find where to look to understand: A) what really mean QIC-02, QIC-11, QIC-24 and what are the [in]compatibility issues. B) how are the tapes physically organized: all about tracks, direction of writing/reading, record gaps, file marks and labels, if any. C) how are the tapes used (on our Suns at least): end of tape detection and processing, tape contents inventory, measurement procedure, density recognition, etc. Somebody would have good pointers?-- ------------------- --------- ------------------------------------------ Francois Pinard "Vivement C.P. 886, L'Epiphanie (Qc), Canada J0K 1J0 pinard@odyssee.uucp GNU!" (514)588-4656; Odyssee R.A.: (514)279-0716 ------------------- --------- ------------------------------------------
drl@backup (David R. Linn) (06/24/88)
In addition to the previous questions about 1/4" tapes, can someone also explain the difference between the tapes used in SUN/Sony workstations and those used in HP workstations? A SUN cannot read an HP tape and vice versa. David David Linn - drl@vuse.vanderbilt.edu (not what's in the header)
fl@crcc.UUCP (Flavio Spada) (07/01/88)
QIC standards have a number (grows with time...). Standards exist for recording forma, cartridge size, adapter to formatter interfacing, etc... A QIC setup consists of: An adapter that interfaces a system bus to a device bus A formatter that interfaces a device bus to the tape unit The device bus physically is a 50 pin cable to which up to four formatters/tape units can be attached. The system bus can be something like the VM, or the AT, or the SCSI. The recording standards are fairly simple. Essentially all the recent ones specify a fixed track size, and a fixed horizontal recording density (tipially 8k bits per inch). What vaies is the number of tracks across the width of the tape. The very first QIC unit (the DEI 20-40MB ones in the ONYX C8002) had four track, which could be read and written independently; current ones have from 9 to 15, arranged in a serpentine. When you load the cartridge the head is moved up and down to locate the first tracks. 15 seems to be the current maximum # of tracks across the width of the tape, and further improvements will have to come from the horizontal recording density. The two most recent standards are for 125 MB capacity and 150 MB capacity; apparently the 125MB standard is a fluke, because the same type of unit can be modified to the 150MB one, and of course one would prefer the latter. The QIC recording format is a stream format; no preformatting of tapes is necessary, data are simply appended to the tape. If the write fails it is repeated by the formatter automatically until it succeeds, i.e. after having passed over a bad section of the tape. This is very different from the 3M/HP cartridges that have the same physical size; these are formatted into discrete records, and a during preformatting a bad block table is written, etc..., just like a disk. This preformatting enables higher recording densities and random access (you can put a unix filesystem on such a cartridge, and it will behave just like one on disk -- but for speed...). It also has a couple of drawbacks, that the format pattern is copyright 3M, so you have to buy their preformatted tapes, and that since the blocks are small (one kilobyte) the tape unit is abysmally slow. The other standards of interest are the QIC standards for interfacing the adapter to the formatter and those for command sequences. They are the QIC-02 and QIC-36 standards. Older units tend to have the QIC-02 interface and newer ones the QIC-36. QIC-36 is somewhat more sophisticated. The command sets are defined like SCSI, a core set of commands, and several optional ones. The core set is truly minimal. Virtually no drive, even the most sophisticated, implement some useful commands, such as backspace record or file, and append to the end of the tape (except in restricted even if useful cases -- too long to discuss). Tape interchangeability is very good -- QIC-24 (9 track) units can read QIC-11 (6 tracks?) ones, and the newer 125/150MB ones can read QIC-24 tapes. Writing with earlier recording formats is usually either not supported or not very reliable. Some obstacle to interchangeability is that adapters occasionally differ as to byte ordering or byte signedness (to read a plexus cartridge on a ncr you must subtract replace each byte by 255 minus its previous value...) but usually writing a simple filter is sufficient. Many adapters differ as to the maximum block size supported; you can safely bet that every adapter will support blocks to 32767 bytes in length, but after that you take your chances (the plexus P55 adapter and its driver will crash the system if you try reading or writing long blocks). As to speed, all recording standards so far specify 90 inches per second that multiplied by the horizontal density gives a maximum thruput of 5 MB per minute. This is rarely attained, in practice, because it requires the adapter to supply data at that rate, and most discs and filesystems and backup utilities have difficulty with that. This emans that the tape will occasionally have to stop recoding or reading, and wait for more data to arrive. The cheap mechaniscs of QIC units imply that stopping will take a long time, and this would waste a lot of tape at each stop, so stopping actuallyis followed by a backspace. In practice the speed of a QIC unit is dominated by the time it takes to stop the tape after each block and that to backspace. Writing long blocks is advisable, because it minimizes the occurence of these actions, and selecting a unit that is quicker at this helps as well, as all other paramters are standardized. I Hope that this long and necessarily skimpy introduction is useful; further details may be found in several back issues of magazines such as EDN, Mini-Micro Systems, etc..., that often (usually every year) publish a survey of current QIC technology and products. Piercarlo Grandi Until 88/JUL/05: ...!mcvax!i2unix!irst!sabi!piercarl sabi!piercarl@irst.it After 88/JUL/05: ...!mcvax!ukc!aber-cs!piercarl piercarl@cs.aber.ac.uk