sandel@TUVALU.SW.MCC.COM (Charles Sandel) (07/17/89)
We have 2 of the Megatape 8mm units. In general, they are good units. We had previously bought 2 Delta Microsystems 8mm units for use on our Suns and the Megatapes were bought to be compatible with them. We had some difficulty getting that to work, but once the bugs were worked out and I understood what was going on, the compatibility issue has been resolved. The Megatapes use the Exabyte drive and add a Pertec interface so that they can "look" like a 1/2" tape drive to the Pyramid. There is no particular speed or reliability advantage to this. The advantage is that it does not require any special software to use. The usual Unix utitilies for magtape manipulation (mt, tar, dump, restore, cpio, dd) work fine. I have found no problems with the magtape emulation of the Megatape. Setting up the Megatape requires you to select the "speed" of its connection to the host computer. This is DIP-switch selectable up to 500KB/sec. For the Pyramid, I found by experimentation that 250KB/sec is optimum. In fact, any higher selection will not work. This is OK, since the drive itself has a upper limit of about 200-250KB/sec transfer anyway. (NOTE: we have a 9825 with the "fast" IOP's. If you have IOC's I suspect you might have to select a lower transfer rate.) There are (as far as I know) 3 recording formats for 8mm tape: 1. Fixed-block size: blocks are written to tape in whatever size you specify. Each block is assumed to be the same size 2. Variable record size: blocks are written to tape including a header which specifies the size of the block 3. "Short" EOF markers: uses short EOF markers; in other modes, an EOF marker uses up 2MB of tape. In short mode, it uses only 1/2 MB, but "skip-file" commands do not work. A tape written in one format (as far as I can tell) is not readable using a different format. The Delta Microsystems boxes will read and write in all 3 formats. The Megatape (as far as I can tell) *always* uses the variable-record-size format. For compatibility, we are always using our Delta boxes in the variable-size format. There does not seem to be any speed penalty associated with this format over the fixed-size format. We are able to exchange tapes between the Delta and Megatape with no problems, assuming we use the same block size. For dumps, using the 4.[23]BSD dump(8) utility, we always use a 32KB block size on all our dumps to both the Megatape and Delta. This is the maximum for the Megatape and always using the same REAL block size assists tape transfer between the different types of drives. NB: the Pyramid dump(8) takes its block specification in 2KB chunks, while the Sun dump(8) takes it's specification in 1KB chunks. Therefore, to get a 32KB blocksize on the Pyramid we specify a block size of 16 to the Pyramid dump(8) program, while the Sun gets a specification of 32 for the same REAL block size. We have had a couple of problems with the Megatape: 1. Setting up is difficult because of the position of the rear cable sockets 2. Setting the DIP switches is difficult because of their placement 3. Deciding on the setting for the transmission speed was by trial-and-error because there was no clear indication of how to determine this (use 250KB/sec). 4. Tech support is not particularly helpful by comparison with other companies (such as Delta) 5. One drive recently died with a tape stuck inside. We had to use the manual door release to get the tape out. Megatape's warranty replacement policy does not include provision for a loaner, so we will be without a drive for about 3 weeks while they fix it. In general, though, I am glad we have the drives. They provide us with the tape capacity we need on our Pyramid. If you do not have Pyramid's SCSI interface (a relatively new product I think), then you will need to look at Megatape and other companies that provide a Pertec emulation with the Exabyte drive. I believe that there is one other company providing the Pertec interface, but I do not know its name. Megatape is not the most responsive company I've worked with as far as technical support (no one seemed to be willing to answer questions for me, and the warranty repair policy is not particularly good), but they are far from the worst. NB: the transfer rate of the Megatape drives on the Pyramid realistically maxes out at about 180KB/sec for backups. This is not particularly fast. With any of the 8mm drives, you must be willing to trade speed for capacity. Charles Sandel MCC/STP Austin, Texas sandel@mcc.com sandel@milano.uucp
miken@mirror.TMC.COM (07/19/89)
Thanks for the informative posting. Question: did you buy your drives through Pyramid or MegaTape?
sandel@TUVALU.SW.MCC.COM (Charles Sandel) (07/24/89)
Our 8mm Megatape drives were bought directly from Megatape, not from Pyramid. I don't believe that Pyramid is selling an 8mm tape drive. Charles