sclubley@compulink.co.uk (Simon Clubley) (07/02/90)
In message <memo.59492@cix.uucp> I asked: >I am currently looking at replacing the backup system on my PDP-11/84 >with a new one. I am looking at the possibility of using DAT or >re-writable optical disks. Has anyone had any experience of using >these backup devices under RSTS (will they even run under RSTS ?) >and what kind of backup performance/reliability problems have you >found ? To which kph@dustbin.cisco.com (Kevin Paul Herbert) replies: >What DEC devices do the optical disk and DAT emulate? Is the optical >disk write once, or write many? > >Kevin Apologies for omitting this information from the original posting. The optical disk is a write-many unit (the Ricoh RO-5030E) and emulates a DU (RAxx) type disk. The DAT is the Sony SDT-1000 emulating a TK50. I am trying to determine whether the performance figures vendors are quoting (3MB+/minute copying from the Fujitsu M2322 drives (emulating an RM02) that I use) are achievable under RSTS/E V9.7 using BACKUP and whether there are any compatibility/data integrity problems. Simon Clubley sclubley@cix.compulink.co.uk
kph@dirt.cisco.com (Kevin Paul Herbert) (07/06/90)
I don't know anything about the specific devices that you are using, but I can give you the general answer. BACKUP beats very heavily on MSCP devices. On your PDP-11/84, BACKUP will probably keep the entire MSCP command ring full for the duration of the backup. Generally, the only time that this doesn't occur is if you run out of Unibus Map Registers (the registers used to map from the 18-bit Unibus to the 22-bit memory bus on newer Unibus PDP-11s), and if this happens, your performance suffers badly. BACKUP has been known to find microcode bugs in controllers which have not been driven that fast before. You should be sure that you have good support from whatever company you buy the controller from, in case they have problems like this. The BACKUP format written to disk is a standard disk file. BACKUP writes to it in random order, dependant upon the order of disk I/O completions from the source device. Some optical disks are designed to be written to in sequential order; your BACKUP performance may suffer as a result. When writing to tape, BACKUP works very hard to sustain high data rates, pausing to "prime the pipe" as an optimization for streaming tape drives where it is more efficient to write fast bursts than slow steady data. I don't know precise the start/stop mechanism is on DAT; you should experiment with the /BUFFER switch to see what works best. I hope this helps you evaluate the products. Kevin |-----------------------------------------------------------------------------| | Kevin Paul Herbert | Use of psychedelics and marijuana leads | | Terminal Server Software Hacker | to greater spiritual understanding and | | cisco Systems, Inc. | the ability to see through propaganda. | | Menlo Park, CA | This is why it is illegal. Any questions? | |-----------------------------------------------------------------------------|