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Self-Repairing Computers
Roland Piquepaille writes "Our computers are probably 10,000 times faster than they were twenty years ago. But operating them is much more complex. You all have experienced a PC crash or the disappearance of a large Internet site. What to do to improve the situation? This Scientific American article describes a new method called recovery-oriented computing (ROC). ROC is based on four principles: speedy recovery by using what these researchers call micro-rebooting; using better tools to pinpoint problems in multicomponent systems; build an "undo" function (similar to those in word-processing programs) for large computing systems; and injecting test errors to better evaluate systems and train operators. Check this column for more details or read the long and dense original article if you want to know more."
Maybe I just don't understand this part. The other points all seem very sensible.
std::disclaimer<std::legalese> sig=new std::disclaimer; sig->dump(); delete sig;
Not to mention that the ROC system itself will need to be rock solid. It's no good to have a recovery system that needs to recover itself, which would then recover itself and so on :)
I wonder if this [PDF!] cool new feature will help there.
Sounds a lot like "micro-rebooting" to me...
my
Here's the strategy:
1. Every system will have a spare 2GB filesystem partition, where I copy all the files of the 'root' filesystem, after successful instln., drivers, personalised settings, blah blah.
2. Every day, during shutdown, users are prompted to 'copy' changed files to this 'backup OS partition'. A script handles this - only changed files are updated.
3. After the 1st instln. a copy of the installed version is put onto a CD.
4. On a server with 4*120GB IDE disks, I've got "data" (home dirs) of about 200 systems in the network - updated once a quarter.
Now, for self-repairing:
1. If user messes up with settings, kernel etc., boot tomsrtbt, run a script to recopy changed files back to root filesystem -> restart. (20 mins)
2. If disk drive crashes, install from CD of step 3, and restore data from server.(40 mins)
Foolproof system, so far - and yes, lots of foolish users around.
If you keep throwing chairs, one day you'll break windows....
they were large telecomms phone switches.
:)
When I left the company in question, they had recently introduced a 'micro-reboot' feature that allowed you to only clear the registers for one call - previously you had to drop all the calls to solve a hung channel or if you hit a software error.
The system could do this for phone calls, commands entered on the command line, even backups could be halted and started without affecting anything else.
Yes, it requires extensive development, but you can do it incrementally - we had thousadnds of software 'blocks' which had this functionality added to them whenever they were opened for other reasons, we never added this feature unless we were already making major changes.
Patches could be introduced to the running system, and falling back was simplicity itself - the same went for configuration changes.
This stuff is not new in the telecomms field, where 'five nines' uptime is the bare minimum. Now the telco's are trying to save money, they're looking at commodity PCs & open standard solutions, and shuddering - you need to reboot everything to fix a minor issue? Ugh!
As for introducing errors to test stability, I did this, and I can vouch for it's effects. I made a few patches that randomly caused 'real world' type errors (call dropped, congestion on routes, no free devices) and let it run for a weekend as an automated caller tried to make calls. When I came in on Monday I'd caused 2,000 failures which boiled down to 38 unique faults. The system had not rebooted once, so only those 2,000 calls had even noticed a problem. Once the software went live, the customer spotted 2 faults in the first month, where previously they'd found 30... So I swear by 'negative testing'.
Nice to see the 'PC' world finally catching up
If people want more info, then write to me.
Mark
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So what are some of the other paradigms which might be proferred instead of von Neumann?
... the biggest problems with existing architectures for self-repair are in the area of keeping track of one thing: time.
My take is that for as long as CPU design is instruction-oriented instead of time-oriented, we won't be able to have truly trusty 'self-repairable' computing.
Give every single datatype in the system its own tightly-coupled timestamp as part of its inherent existence, and then we might be getting somewhere
Make time a fundamental to the system, not just an abstract datatype among all other datatypes, and we might see some interesting changes...
; -- the corruption of government starts with its secrets. a truly free people keep no secrets. --
Wouldn't some sort of software solution be the Hurd (if/when it becomes ready) in that as each system is a micro-kernel you just restart that bit of the operating system. As said in another post this is like /etc/rc.d but at a lower level.
Or you could just have some sort of failover setup.
Rus
Cheap UK and US VPS
My particular system of research finally wound up relying on the Windows method: if uncertain, erase and reboot. It didn't have to be 99.999% available, after all. There are other ways with which to solve this in distributed/clustered computing, such as voting: servers in the cluster vote for each other's sanity (i.e. determine if the messages sent by one computer make sense to at least two others). However, even not this system is rock solid (what if two computers happen to malfunction in the same manner simultaneously? what if the malfunction is contagious? or widespread in the cluster?).
So, self-correcting is an intriguing question, to say the least. I'll be keenly following what the ROC fellas come up with.
well the man who answers this question will certainly become the von Neumann of the century, you need to do some serious out of the box thinking, first you throw away the concept of the digital computer as you know it, personally I think there will be a split in computer science, there will be generally two computer types the "classical" von Neumann and a new and different type of computer, the classical computer will be useful as a controller of some sort for the newer one, it is difficult to come up with the working principle of that computer, let me elaborate it is like a missing piece of the puzzle you know how it looks like but you are not certain what exactly will be printed on it, but I can summarize it is features: ..Etc
Finally well such a computer be useful? can we just write a plain spread sheet on it and send it by email to someone and then resume our saved DOOM game?
1. It must be data oriented with no concept of instructions (just routing information), data flows in the system and transformed in a non-linear way, and the output will be all possible computations doable by the transformations.
2. It must be based on a fully interconnected grid of very simple processing elements.
3. The performance of said computer will be measured in terms of bandwidth not the usual MIPS. As you can see you will need a classical type computer to operate the described computer above so it will not totally replace it.
I believe that we should look into nature more closely, we stole the design of the plane straight from birds wings, and the helicopter from the dragonfly, and there are a lot that was inspired to us by mother nature, one of the relevant examples that always fascinated me was the fly brain, each eye is a processor on its own, the works independently conveying information to a more concise layer and so on, even human vision is based on similar concept of retina cells, there is no "pixel" concept, each layer that process vision emphasize on one concept of vision like texture, color, outline, shadowing, movement...etc
well it is possible but we need also to redefine what we can do with a computer because the classical von Neumann computer that we are stuck with for the last half a century certainly limited our imagination on what can be done with a computer.
There are allready steps in place towards recoverability in currently running system. That's what filesystem journaling is all about. Journaling doesn't do anything that fsck can't do EXCEPT that replaying the journal is much faster. Vi recovery files are another example. As the article pointed out, 'undo' in any app is an example.
Life critical systems are often actually two seperate programs, 'old reliable' which is primarily designed not to allow a dangerous ondition, and the 'latest and greatest' which has optimal performance as it's primary goal. Should 'old reliable' detect that 'latest and greatest' is about to do something dangerous, it will take over and possibly reboot 'latest and greatest'.
Transaction based systems feature rollback, volume managers support snapshot, and libraries exist to support application checkpointing. EROS is an operating system based on transactions and persistant state. It's designed to support this sort of reliability.
HA clustering and server farms are another similar approach. In that case, they allow individual transactions to fail and individual machines to crash, but overall remain available.
Apache has used a simple form of this for years. Each server process has a maximum service count associated with it. It will serve that many requests, then be killed and a new process spawned. The purpose is to minimize the consequences of unfixed memory leaks.
Many server daemons support a reload method where they re-read their config files without doing a complete restart. Smart admins make a backup copy of the config files to roll back to should their changes cause a system failure.
Also as the article points out, design for testing (DFT) has been around in hardware for a while as well. That's what JTAG is for. JTAG itself will be more useful once reasonably priced tools become available. Newer motherboards have JTAG ports built in. They are intended for monitor boards, but can be used for debugging as well (IMHO, they would be MORE useful for debugging than for monitoring, but that's another post!). Built in watchdog timers are becoming more common as well. ECC RAM is now manditory on many server boards.
It WILL take a lot of work. It IS being done NOW in a stepwise manner. IF/when healthy competition in software is restored, we will see even more of this. When it comes down to it, nobody likes to lose work or time and software that prevents that will be preferred to that which doesn't.
Do we have to keep using this tired old notion of little old (middle-aged, for the /. crowd) ladies cringing in terror when faced with a computer?
My mother has a B.Math in CS, acquired more than a quarter century ago. Her father is pushing eighty, and he upgrades his computer more often than I do. When he's not busy golfing, he's scanning photographs for digital retouching. (In his age bracket, a man who can remove double chins and smooth wrinkles is very popular.)
The notion that women and/or the elderly are unable to use computers is a generalization that just doesn't hold much water anymore. Maybe some of these people are frightened of (or frustrated with) computers because their exposure to technology is through the 'typical'* arrogant, smug, condescending /.er--concealing his embarrassment over being unable to get a girlfriend behind clouds of technobabble.
*How does it feel to be the target of an unfair stereotype?
~Idarubicin
The software that I'm responsible for, in fact, is specifically designed to detect, report, and try to work around errors. We have code to detect a processor hang (through software or hardware failure) and remove it from the running OS image, etc. The Cray T3E (which I didn't work on) can warm-reboot an individual processor on either a software or hardware panic/hang and reintegrate it into the running OS.
Go Badgers! -- #include "std/disclaimer.h"