esd@liebert.uucp (Eric Scott Deese) (06/12/90)
I am experiencing a problem for which I quickly need an explanation/solution. We are running SCO UNIX 3.2 on IBM PS/2 model 80 machines. On seperate machines, we have an Irwin 80 MByte mini-cartridge tape and an Archive 60 MByte tape (DC600 type cartridges). On each system, at various times, we attempt a backup to tape (via cpio or tar) and receive a message from the tape driver : "not enough memory". A call by our sister company to SCO received the solution of "add more RAM". That system had 4 megabytes and received the error (almost) always. That system was upgraded to 8 megabytes and has not received the error since (for the last week or two). A machine here has 6 megabytes and receives the error sporadically for as long as I can remember. The problem can be alleviated by logging off users and/or terminating running processes. Current theory is: Since the tape controllers utilize DMA (we assume), the tape controller requests a chunk (how big I really want to know) of CONTIGUOUS memory, which only gets satisfied for a large RAM size or sparse utilization by other processes. 1) Is this theory correct? 1a) If correct, two possible solutions : - Build a buffer into the tape driver that it gets upon system boot and keeps forever. What a pig, BUT a solution I am willing to live with to get reliable tape access. - Make the tape driver force the kernel to give it a contiguous buffer. If that means swapping other processes, then fine, just do it. 1b) If correct, is there a non-DMA tape controller (such as SCSI for Archive tapes) that would solve the whole problem? 2) If the above theory is incorrect, what is the real explanation? Our experiences indicate this occurs sporadically based upon memory utilization by all processes in the system. How do you know when you have enough memory? All of this is a REAL PROBLEM for our two companies. We are prepared to begin shipping a turnkey application based upon SCO UNIX and some tape drive. We MUST have a system that can perform a tar or cpio at any time. The application is not such that we can simply say "Kill off some processes and try the tape again". We need a real solution, and we need it fast. Any ideas/soultions/answers greatly appreciated. Input is welcome from SCO, Irwin, Archive, other tape vendors and other operating system vendors. But don't let this stop you. If you know the answer, PLEASE let us know. Thanks, Eric Deese (osu-cis!liebert!esd) (614) 841-5508