[TUHS] Ultrix Tape: Block Size?

#$%^ - they >>weren't<< like DECtape from a reliability standpoint ... ? On Mon, Oct 15, 2018 at 5:00 PM Clem Cole <clemc at ccc.com> wrote: > Be careful, TK-50 is different than 9-track. It's a streamer tape like > QIC, 4mm and 8mm. The blocking is done under the covers by the HW and the > blovk size if just how a DMA is done. I recommend that you pre-fetch the > read with dd or double-dd setting ibs=64k, obs=20b and conv=sync and pipe > the output to the reader (tar/cpio or the like) [if that fails try > obs=1b]. This should work well as can (TK-50 overall suck - don't set > your hopes high on anything with them -- they were DECtape from a > realiabilty standpoint, they were different from the reset of the world, > the performance was poor and they were expensive). > > Anyway, by using dd or the like a front end, it will allow the read > streamer to read as fast as it can. The problem is that the way it works > under the cover does not shine with traditional UNIX I/O. BTW: ibs of > anything more than 64K on a VAX (or PDP-11) will not help because of the > dma size on the Unibus caps DMA read/writes at 64K. On a PMAX or (under > Tru64 on a Alpha), you can try using really large ibs sizes depending on > your physical memory size. > > BTW: What will help the most is actually finding a copy of the old > double-dd program (from the UUNET archives) which forks off two child > procees to perform the actual I/O and alternates between the two processes > via pipe between them and controller - so one dd process is reading when > the other dd process is writing. [It used to be called: ddd before the > Gnu guys grabbed that name for the debugger]. The command line might be > something like: ddd ibs=64k obs=20b | tar xvpf - > > FWIW: I wrote a version of a fast dd years ago that used pthreads and a > semaphore that I should still have kicking around. At one point when I > was dealing with streamer tapes for backup, I definitely ran it on Tru64 > and FreeBSD, but I've forgotten where Ultrix fell. > ? > > On Mon, Oct 15, 2018 at 4:01 PM Warren Toomey <wkt at tuhs.org> wrote: > >> All, I received this request from Matthew who isn't subscribed to either >> the TUHS or cctalk lists. He knows how to read the lists archives. Many >> thanks for any help you can provide. >> Cheers, Warren >> >> ----- Forwarded message from Matthew Whitehead ----- >> >> Date: Mon, 15 Oct 2018 08:25:39 -0400 >> From: Matthew Whitehead >> Subject: Ultrix Tape Blocks >> >> Warren, >> I wonder if you can give me a referral. I want to install Ultrix-32 >> on my MicroVAX II using the ancient TK-50 tape drive. I know the tape >> files are on your archive, but I need to know the block size for each >> of the many files; it can vary a lot. >> Who might be able to help me with this? >> Matthew Whitehead >> >> ----- End forwarded message ----- >> >