avg@hq.demos.su (Vadim G. Antonov) (09/02/90)
> > MTBF(controllers) >> MTBF(disks) > I have no idea about this statement but I sure that MTBF(software) << MTBF(disks) is true. I used to work on machines failing several times a day due to hard CPU errors, with disks reporing CRC errors one time per 100 i/o requests and containing "floating" bad sectors. Original Unix could not work on my machine even a quarter of hour (it was really failing!). But I haven't lost a byte of my information during several years. So, if you like to keep your data on-line you should choose a better scheme than mirroring because it't QUITE USELESS against software (and software-related like an improper handling of power faults) bugs. The only way to protect yourself against software failures is to keep your data IN DIFFERENT FORMATS. I mean file-by-file dumping etc. Another important thing to do is to design a REAL error handling in drivers - for example, a disk driver should check controller's internals as much as possible. The Unix drivers is usually designed without keeping such things in mind. And last (but not least) thing is a fault-tolerant file system. Sys V format is NOT fault-tolerant. BSD systems behave a much fairly. Some things in Unix are REALLY dangerous - like a writing access time stamp directly into inode. "Unmodifyed information should be kept unchanged". An experimental fact: if you'd hack out writing i_atime your system will be 10-20% more reliable. NEVER use software w/o source codes - it gives you no chance to improve reliability of your installation. > ...I'm not cynical - just experienced. So, my private opinion is that the mirrored disk is not the best and VERY expensive vehicle to carry your bits on. :-) Regards, Vadim Antonov, DEMOS, Moscow, USSR (It is NOT a joke!)
gary@sci34hub.UUCP (Gary Heston) (09/11/90)
In article <1990Sep2.112938.4462@hq.demos.su> avg@hq.demos.su (Vadim G. Antonov) writes: > [ several pieces of reasonable advice deleted ] > NEVER use software w/o source codes - it gives you no chance > to improve reliability of your installation. I'm curious, Vadim. What operating system do you use? All of them I've dealt with, the vendors didn't consider releasing the source code. There are a few real limited OSs distributed as public domain or shareware, but I don't think there are many sites using Minix or Xinu commercially. Certainly, AT&T hasn't generally released the source for UNIX without a (expensive) license; Microsoft to my knowledge hasn't licensed source to more than a couple of repackagers, and DRI never released source for any version of CP/M or DR-DOS. There are limits to what you can get. If you were seeing "hard cpu errors", I'd suspect the cpu chip or board, more than the OS. -- Gary Heston { uunet!sci34hub!gary } System Mismanager SCI Technology, Inc. OEM Products Department (i.e., computers) "The esteemed gentlebeing says I called him a liar. It's true, and I regret that." Retief, in "Retiefs' Ransom" by Keith Laumer.