Amazon Explains Why S3 Went Down 114
Angostura writes "Amazon has provided a decent write-up of the problems that caused its S3 storage service to fail for around 8 hours last Sunday. It providers a timeline of events, the immediate action take to fix it (they pulled the big red switch) and what the company is doing to prevent re-occurrence.
In summary: A random bit got flipped in one of the server state messages that the S3 machines continuously pass back and forth. There was no checksum on these messages, and the erroneous information was propagated across the cloud, causing so much inter-server chatter that no customer work got done."
for want of a nail ... (Score:5, Interesting)
Re:for want of a nail ... (Score:5, Funny)
It was the evil bit...
haha (Score:5, Informative)
Re:haha (Score:1)
Re:haha (Score:3, Informative)
Re:for want of a nail ... (Score:0)
"Amazon has provided a decent write-up of the problems that caused its S3 storage service to fail for around 8 hours last Sunday. It providers a timeline of events, the immediate action take to fix it (they pulled the big red switch) and what the company is doing to prevent re-occurrence. In summary: A random bit got flipped in one of the server state messages that the S3 machines continuously pass back and forth. There was no checksum on these messages, and the erroneous information was propagated across the cloud, causing so much inter-server chatter, that no customer work got done."
I wish I could be a /. editor and get paid for not doing jack shit all day.
Re:for want of a nail ... (Score:2)
It's like a self-replicating virus that arose from the result of a random mutation.
"Ever since the first computers,
there have always been
ghosts in the machine.
Random segments of code that
have grouped together to
form unexpected protocols."
Re:for want of a nail ... (Score:3, Funny)
1 million code monkeys typing out Aleister Crowley?
Re:for want of a nail ... (Score:1)
BOFH, obviously. duh. and quite cleverly disguised.
evil bit defined (Score:1)
Re:for want of a nail ... (Score:0)
Computer Networks by Andrew S. Tanenbaum [amazon.com]
Well there is some reading for them.
Re:for want of a nail ... (Score:5, Informative)
Re:for want of a nail ... (Score:4, Interesting)
re:Northeast Blackout of 1965 (Score:2)
I thought that was caused by the bouncy-ball "gift" from the Great Collector. (He thought it was funny as hell....)
Re:Northeast Blackout of 1965 (Score:1)
I thought that was caused by the bouncy-ball "gift" from the Great Collector. (He thought it was funny as hell....)
He apparently thought we WERE hosting an intergalactic kegger down here.
ECC memory, anyone? (Score:4, Interesting)
I hafta wonder if the bit flipped due to a bad RAM stick?
Nothing specific about *what* caused the bit to flip.
This comes to mind only because bad RAM on a new server at work caused installation of a stock Perl module to throw excessive errors during the XS compile phase - the same package installed without error on an identical machine 20 minutes earlier. Took over an hour before we realized it was probably hardware. Memtest86 [memtest86.com] quickly turned up the problem.
Would hashes and the like protect against RAM suddenly going south? Wouldn't any piece of data that passes through main memory be vulnerable to corruption? Makes me wonder why ECC memory [wikipedia.org] isn't being used much anymore... we have various flavors of RAID to protect slow memory from corruption, but not many machines I see have ECC anymore.
Re:ECC memory, anyone? (Score:4, Informative)
Re:ECC memory, anyone? (Score:5, Informative)
No, that's just one kind of memory system. There are a number of designs, and recovery also depends on the kind of error. IIRC, one design is somewhat similar to the CD Red Book spec, in that the bits for a given byte are distributed around - a physical byte is composed of bits all from different memory locations. If part or all of one byte goes bad, the rest of the bits and the parity code are unchanged, and the affected bytes can be reconstructed.
Also like Red Book CDs are multiply redundant memory systems, with -just what it sounds like- multiple copies of each byte, and the memory controller arbitrates differences. CDs effectively contain three copies of the data, striped and parity encoded. That's how scratched CDs can still operate error-free (sometimes.) The space shuttle's computer systems are relatively fault-tolerant - multiple redundant computers all running the same programs and data, with a fourth computer evaluating the output of the other computers, looking for failures.
Where there's a will, there's a way, but the will in the mainstream x86 server industry to build truly fault-tolerant computers is slim. It's a specialty, and that makes it very expensive. Stratus [stratus.com], for example, makes a line of fault-tolerant servers [stratus.com], with some of the fail-over in hardware, so they make their 99.999% uptime claim (about 5 minutes downtime per year.)
"Five nines [wikipedia.org]" is a claim I've heard from most top-dollar *nix hosting companies, but have *never* experienced - it's generally been hours of downtime per year. Not even their network infrastructure gets close to 99.999% uptime! Cadillac prices, but downtime contingency planning is all up to the client, even with "managed hosting." They all suck.
Re:ECC memory, anyone? (Score:3, Informative)
Red Book audio CDs, Sony MiniDisks and DATs all use a form of Cross-Interleaved Reed-Solomon [wikipedia.org] coding, which is has the nice characteristic of being able to use the fact that a piece of information is known to be missing when reconstructing the original signal, whereas other systems can't necessarily be improved by being informed of the difference between an "error" and an "erasure." Side information about "known-bad" media areas are a natural fit for physical media, not necessarily for serial data or other things.
CDs also have parity bits on every (EFM-encoded) byte on the media, which can contribute to the "erasure" side-information along with tracking data from the laser. Also working in the CD's favor is the fact that they carry relatively low-information PCM data, and if there is a complete loss of a sample or two, the decoding device can just do a 1st order interpolation between the surrounding known good samples. This is why CDs can sound excellent until one day it might just not play at all, without an significant period of declining quality, because errors were accumulating until you reached a critical point where your player couldn't spackle over the errors anymore, and it juts gives up.
only ot fyi :)
Re:ECC memory, anyone? (Score:2)
That's a really interesting distinction. If I'm reading right at this hour, you're saying that the read device is able to distinguish between on, off and bad media? Something a RAM chip or memory controller can't do, I imagine, because it's receiving a signal from deep inside ... good or bad, the media's read indirectly.
FSM-damn, there are knowledgeable folk here on /.
Re:ECC memory, anyone? (Score:3, Informative)
Re:for want of a nail ... (Score:0)
It's called a "flag", in case you didn't know that.
Re:for want of a nail ... (Score:2)
A flag can be stored as a bit, but not all bits are used as flags..
Re:for want of a nail ... (Score:0)
I guess a little bit goes a long way.
Re:for want of a nail ... (Score:0)
with at least 2 wrong 'bits' just in the summary imagine the horror of the S3 codebase!
Re:for want of a nail ... (Score:1)
For want of an unflipped bit a server was lost.
For want of a server gossip was lost.
For want of gossip clusters were lost.
For want of clusters revenues ceased.
All for want of an unflipped bit.
You have no idea... (Score:1, Interesting)
As someone who worked at Amazon as a software engineer for over three years in various backend areas, I can say that without a doubt, Amazon's code and production quality is so horrible, that it's hard to believe.
Engineers carry pagers and, in many groups, are constantly paged. The only thing that keeps the systems running is a bunch of junior engineers responding in the middle of the night, fixing databases, bouncing services, etc., etc. Engineers are rarely, if ever, given the chance to actually *fix* things, they're just supposed to band-aid them up.
And, here's a big secret for you: When I left Amazon a little over a year ago, no development groups internally were even using EC2, S3, SQS, or any of the other web services they sell to you. They make it sound like you're using the same high-end services they use to satisfy tens of millions of customers. They're not.
Re:for want of a nail ... (Score:5, Funny)
"On Sunday, we saw a large number of servers that were spending almost all of their time gossiping and a disproportionate amount of servers that had failed while gossiping. With a large number of servers gossiping and failing while gossiping, Amazon S3 wasn't able to successfully process many customer requests."
sounds like a restaurant, gossiping servers were failing to process customer requests
They need more Erlang. (Score:0)
They need to start using Erlang more. It's designed specifically for building highly-distributed, concurrent systems that must scale to millions of transactions per minute. So it's a natural fit between Erlang and what Amazon is trying to offer with their S3 service.
Re:They need more Erlang. (Score:5, Insightful)
They need to start using Erlang more. It's designed specifically for building highly-distributed, concurrent systems that must scale to millions of transactions per minute. So it's a natural fit between Erlang and what Amazon is trying to offer with their S3 service.
I think Erlang's cool and all, but it's not the magical bullet that will solve this. It's still possible to have information corrupted during message passing between processes in Erlang (say, as the result of an intermittently failing network switch) as it is in any language.
Re:They need more Erlang. (Score:0)
Re:They need more Erlang. (Score:5, Insightful)
Erlang or any other functional language will not account for lack of good design. If you have a good design with the right concerns you can implement in Java, C, Fortran, ASM and if done right, it will work.
I'm sick of hear "Erlang is THE solution". It is not. Good design and implementation practices are.
Simple (Score:3, Insightful)
S3 is a total slut.
Re:Simple (Score:2)
Aw. And it appears that this has been posted from the not-mere-sluttiness dept. It appears that slashdot editors already stooped to the lowest from of humor in posting the headline, and I've just fallen into their redundancy trap. Tricky, tricky!
It's not the first time... (Score:0)
A random bit got flipped
...that a bit on the side has caused problems.
Look at Max Mosely, for example.
...make lemonade. (Score:4, Funny)
Cosmic Rays perhaps? I guess they could line the room with lead, or simply re-market S3 as a Neutrino detector [wikipedia.org]. :-)
Re:...make lemonade. (Score:3, Insightful)
Or they could checksum their UDP packets. The entire packet, not just the customer payload. Duh.
Re:...make lemonade. (Score:3, Interesting)
There's probably information that changes as the packets move around, and they probably wanted to avoid the overhead. I'm guessing it was a deliberate design decision, but it turned out to be the wrong one. It's easy to see that after a failure, but it's hard to design large distributed systems and foresee every possible way things can break, and where the computation overhead is worth it. The number of interactions between servers here makes any small design flaw a big thing.
Re:...make lemonade. (Score:1)
Re:...make lemonade. (Score:5, Insightful)
No, I mean favoring speed and computational simplicity over error detection.
It is often a valid trade off. For example, most filesystems do not validate the stored data at all for size and computational reasons. As hard drives and arrays get bigger, that trade of no longer makes much sense, and most all new filesystems being designed have hash based error detection built in at some level.
Good design takes experience. There aren't that many systems like S3 that have been built in the past, and there are many tricky decisions to be made. No system gets it all correct out of the gate.
Re:...make lemonade. (Score:1)
Or they could use TCP.
Re:...make lemonade. (Score:2)
It is quite simple to prove mathematically, that it is in general impossible to devise a protocol that guarantees 100 percent correctness of a signal on an independable line.
(You simply do it by recursive reduction: If the protocol works even if the last bit is missing, then you could send the message without the last bit anyway. If the second last bit can go missing without damaging the integrity of the message, you can leave out that one also... etc.pp. until you don't need to send any bit at all to deliver your message ;) )
Re:...make lemonade. (Score:3, Insightful)
True, but not particularly informative. The point is to detect errors. Error correction is nice, but error detection is enough if the sender can then retransmit. Oh, and your 'proof' is flawed, since you are completely ignoring the fact that any correction scheme contains redundant information, so the while n bits might work instead of n+1 bits, n-1 might not.
If the last bit is missing, then your receiver knows that there is an error. If the last bit is flipped, then it knows that there is an error. A checksum can be very simple and just give the count of the number of bits that are set in the message. This will protect from single-bit errors, but an error in both the message and the checksum can cause an erroneous packet to pass. It's basically a hash, and the idea is to make sure that hash collisions are as infrequent as possible.
You can usually guarantee a maximum number of errors in the network and it's possible to design correction schemes which will detect any n-bit error.
In some cases, it's possible to accurately detect all errors because all failures will be in one direction (0 to 1 or 1 to 0, but not both). In this case, and XOR'd copy of the message will work, because any bit in the message flipping from 0 to 1 needs a corresponding bit in the check flipping from 1 to 0 (there are shorter encoding schemes that work in this case too, but this is a very simple example).
Re:...make lemonade. (Score:5, Interesting)
I see you completely miss the point of the proof. I know that you can minimize the impact of a bit error by checksums, and that you can improve reliability by adding redundance. But what is the consequence of error detection? Normally the protocol then asks for resending the message. But how do you (as the sender) know that the message finally arrived correctly? You wait for an aknowledgement. But what if the aknowledgement gets lost or scrambled? You add redundancy in the handshaking. But how does redundancy help reliability? You can ask for a resend due to detected errors etc.pp.
Your protocol never finds an end because it has to secure the correctness of the security of the correctness of the security...
Re:...make lemonade. (Score:2)
It's called the Two Generals' Problem [wikipedia.org].
Re:...make lemonade. (Score:1, Interesting)
That there's nothing you can do to get the correct message to the other end if the lower level connection doesn't send anything (e.g. someone unplugged the ethernet cable) or corrupts everything sent, is spectacularly uninteresting.
What people actually care about it given a connection with some statistical level of unreliability you can build a reliable connection out of it. The less reliable the real connection the more overhead you need. Obviously the "reliable connection" isn't actually perfectly reliable if the underlying connection doesn't meet the reliability level that was assumed.
Re:...make lemonade. (Score:2)
Or they could checksum their UDP packets. The entire packet, not just the customer payload. Duh.
Not a network engineer, but I believe that UDP packets contain the source MAC address. When a router receives that packet, it will blow away that MAC address, replace it with it's own, and forward it out the right interface. (This is assuming they're using UDP, TCP/IP, or something else entirely to transmit whatever state fields were corrupted.)
If they did checksum the entire packet, they would have to rebuild the sum at every node to account for the changing MAC address, and who knows what else is modified in the packet header between nodes. This smacks of a lot of wasted processing time, times, like, a metric internet or two.
If it did get corrupted in transmission (not due to faulty memory, as some speculated, or due to evil gremlins or something else) then maybe adding a checksum just to the state bits would be worthwhile.
Re:...make lemonade. (Score:2)
Re:...make lemonade. (Score:2)
Interesting. And who knows how the failed bit got toggled anyway? Perhaps the checksum would have been built around the bad information anyway, and all the other machines would have picked it up as valid.
Lost time? (Score:2)
By 11:05am PDT, ..., the system's state cleared.
At 2:57pm PDT, Amazon S3's EU location began successfully completing customer requests.
So WTF happened during the four hours between 11:05AM and 2:57PM?
And... have they learned nothing from the TIBCO fiasco?
Re:Lost time? (Score:0)
That's how long it took things to come back online.
Re:Lost time? (Score:1, Interesting)
That's how long it took things to come back online.
Well that explains everything. I suppose I should expect that since it goes to 11....
Four hours is a Longgg time... and it was five hours for the US.
Why did it take four hours? Why not 40 minutes or four days?
There is a big hole in the story.
Re:Lost time? (Score:3, Informative)
sun enterprise and most other enterprise servers takes 30-45 minutes to pass the prom tests after you start them up. thats per server, before you even boot the os. my guess is they brought up servers in large batches of 25% at a time and took about an hour per batch.
Re:Lost time? (Score:5, Informative)
Read "the system's state cleared" as "we turned everything off" and they proceeded to turn every server on one by one until around 3PM when the EU location was complete and not showing any symptoms.
Re:Lost time? (Score:1)
They programmed a checksum into their message-passing?
Other companies could learn from this... (Score:5, Insightful)
Other large businesses could learn a lot from Amazon's example.
How often do you have the problem really explained to you, an apology, and a reasonable set of changes to stop it occurring again?
Most businesses would never explain the root of any problem. They simply list "hardware issues." And they NEVER say sorry anymore - supposedly it opens them up to more liability or something.
If I was an Amazon customer I would be happy with their explanation and apology even if obviously the downtime is still an issue.
Re:Other companies could learn from this... (Score:2, Insightful)
Looking back, I feel that the one thing all our technological progress has given us more than anything else, is more and better means of communication.
You can talk to people on the other side of the world, heck, on the other side of the solar system if you don't mind the delay. Video feeds, planes that'll actually get you there in less than a day, ...
And yet, with all of this, it seems that we're not actually doing it. A company explaining what went wrong is the exception. Internet forums without flamers and trolls? Exception.
"Anything you say can and will be used against you."
Re:Other companies could learn from this... (Score:5, Funny)
Other companies could learn something from this, unfortunately they won't be able to do anything similar as Amazon has patented the process of explaining technological problems to customers.
Re:Other companies could learn from this... (Score:0, Offtopic)
Since their drive towards Amazon Prime, their deliveries have been appalling (at least in the area of the UK I'm in), YMMV. As much as I appreciate their candour, the delivery and delay problems are what is driving me away at the moment.
Comment removed (Score:2)
Re:Other companies could learn from this... (Score:2)
It's quite an old story - see RFC789 (Score:5, Interesting)
Vulnerabilities of Network Control Protocols: An Example [ietf.org], published in January 1981.
What do they say about those who ignore history?
Re:It's quite an old story - see RFC789 (Score:5, Funny)
[...]
What do they say about those who ignore history?
I think it was, they're doomed to reimplement it... poorly. Or was that Unix? ;)
Re:Other companies could learn from this... (Score:3, Insightful)
Well, technically speaking, there isn't an apology there:
Finally, we want you to know that we are passionate about providing the best storage service at the best price so that you can spend more time thinking about your business rather than having to focus on building scalable, reliable infrastructure. Though we're proud of our operational performance in operating Amazon S3 for almost 2.5 years, we know that any downtime is unacceptable and we won't be satisfied until performance is statistically indistinguishable from perfect.
Allow me to translate:
We screwed up. We'll do better next time.
Nowhere in the document do the words "I'm sorry" appear. That's entirely implied.
Re:Other companies could learn from this... (Score:5, Insightful)
The words may not be there, but there is a pretty clear message there for me to see that they are not happy or smug about this event, and are agreeing with the consumer that this shouldn't have happened, and won't happen again if they can help it. That's enough for me.
And I'm actually one of their consumers, compared to some of the dilletantes here. We use S3 and EC2 to manage training and demo instances of our software, and are pretty pleased so far.
Re:Other companies could learn from this... (Score:2)
I am a customer, and this does reassure me.
It is sad, though, that it has to go through legal first.
Re:Other companies could learn from this... (Score:2)
Ya, seriously.. Honesty!! In this post-911 day and age, we have honesty!
I'm gonna go buy something from Amazon.com now.
Re:Other companies could learn from this... (Score:1)
I agree. A little transparency goes a long way toward reinforcing credibility. This is a very smart business move. It demonstrates two things. Amazon respects its customers enough not to insult them with some lame, vague 'hardware problem' excuse. And it validates that they actually troubleshoot their problems and understand them before they apply a solution. The combination of these two responses makes the apology even more sincere.
It was drunk, had father issues, and... (Score:1, Funny)
was trying to hold onto a man?
I'm just guessing here.
Sigh. Tempus fugit, and experience is lost (Score:1, Interesting)
I remember at least one similar incident:
Early (or earlish) arpanet, the network controllers did not implement checksum on messages. A bit flip caused the whole shebang to keep on forwarding the same message over and over, to the point that nothing else would flow, not even a reset command. Some one had to be sent to the culprit box and manually reset it.
I remember this being discussed on some technical circles for a while (I think Software Engineering Notes from the ACM had a go on it).
Programmers never learn... (Score:0)
Stop making protocols whereby one server can crash [soft.com] another already. Especially when they talk to each other constantly and there's a lot of them. Cascade failures, FTW.
Re:Programmers never learn... (Score:2)
In 99.9% of cases it isn't the protocol that causes a server crash and instead it is the way that the protocol is implemented.
This story is another example of that. Although they're fixing it by changing the protocol spec' that is really just a much cheaper way of resolving the core issue (e.g. That any input shouldn't ever cause a crash - corrupt or otherwise).
Programmers need to learn something but I think the real lesson here is simply that input over the network cannot ever be trusted. You should assume that it is corrupt, untrusted, or wrong.
Re:Programmers never learn... (Score:0)
"I think the real lesson here is simply that input over the network cannot ever be trusted. You should assume that it is corrupt, untrusted, or wrong."
Isn't this Microsoft's answer?
Deny or Allow?
Oh wait. Replace input over the network with end user?
Re:Programmers never learn... (Score:2)
No. Even if the end user is not malicious or stupid, the network itself will not always transmit accurately. Interference or signal degradation on the lines, or a dodgy switch can screw things up.
Re:Programmers never learn... (Score:2)
Programmers need to learn something but I think the real lesson here is simply that input over the network cannot ever be trusted. You should assume that it is corrupt, untrusted, or wrong.
Well, I have to say I'm guilty. I just assume that all the checksums at the various levels of TCP/IP make sure the data that comes over a socket is the same as what went in.
Of course, if I was working on a critical/must-never-go-down system, I'd maybe be a little more paranoid.
Re:Programmers never learn... (Score:4, Interesting)
I think the real lesson here is simply that input over the network cannot ever be trusted.
It is their network, and S3 is built on tech which is explicitly designed to not have any kind of security built-in. The security is applied at the API level, but any misbehaving machine within the S3 cluster could cause some serious damage.
I actually agree with this philosophy, to an extent. After all, this is essentially a large number of computers acting as a hard disk. How would you approach talking to a hard disk in your own machine? Do you assume that everything is corrupt, untrusted, or wrong?
Re:Programmers never learn... (Score:2)
Re:Programmers never learn... (Score:2)
Yes, or at least we should.
Let me be more specific:
ZFS assumes everything could be corrupt. It makes no assumptions about wrong or untrusted. ("Wrong" being defined here as human error, so that it's not just "corrupt".) And I think that's about all a storage layer should do.
ZFS also isn't the only way to do this. It's perhaps the slickest, but there's still things like the bad-block relocation layer in Linux, and there are higher-level software layers, like Git.
Now, yes, S3 dropped the ball -- there was a point where they missed "corrupt" on that checklist. But I can see how they might have made the simple leap from "trusted" to "assumed non-corrupt".
Also: Consider that this is not the data. This is the communication layer. You might well assume that your data is fine, but what about your northbridge? How do you know the data in RAM is good? (Does ZFS make any allowances for that?)
It was a design defect (Score:5, Informative)
It has been generally well-known for a number of years now that any time you have a large cluster you cannot count on hardware checksums to catch every bit flip that may occur during copies and transmission, particularly with consumer hardware which has many internal paths with no checksums at all. Google learned this the hard way, like the supercomputing people before them, and now like Amazon after Google. And some of the better database engines also do their own internal software checksums as well to catch uncaught errors introduced as the data gets copied across the silicon, disks, and network -- it is one way they get their very high uptime and low failure rate.
It does not reflect well on the software community that most people *still* do not know to do this for very large scale system designs. The performance cost of doing a software CRC on your data every time it is moved around is low enough that it is generally worth it these days. If your system is large enough, the probability of getting bitten by this approaches unity. Very fast implementations of Adler-32 and other high-performance checksum algorithms are widely available online.
Re:It was a design defect (Score:5, Interesting)
Adler-32 wouldn't be a great choice. It's fast but it's weak for short messages [ietf.org] and I've seen it fooled by multi-bit errors on large messages too.
See Koopman's paper 32-bit cyclic redundancy codes for Internet applications [ieee.org] for some better ideas.
Re:It was a design defect (Score:2)
For these purposes, a CRC that is fast and weak is generally superior to one that is slow and strong because the CPU load of the implementation does have a measurable impact on system performance. Remember, the software CRC is supposed to catch failures in the other layers of CRC and error detection, so it does not have to be perfect. If it reduces the probability of an uncaught problem from a few times a year to a few times per millenium, that may be sufficient if using a stronger CRC means burning 10% of your total CPU time. Adler-32 is an example of an algorithm that is used in practice in preference to stronger, slower algorithms, hence why I mentioned it. If there is something as fast or faster that is also stronger, we should be using that instead.
Many of the software checksums used are intentionally weak and fast to minimize the performance impact, though as systems get bigger they may need to use something stronger to keep the probability of an uncaught error within the acceptable safety margins. Fortunately, people are working on that problem.
Re:It was a design defect (Score:5, Interesting)
I've seen Adler-32 fail twice, so your assumption of "a few times per millennium" doesn't seem to work for me (I'm under 40). In fact in those cases it was even stacked on top of at least one other checksum mechanism, too.
One of the problems with it is poor spreading of the input bits into s2. There are other algorithms which don't have that weakness but don't (IIRC) cost any more to compute.
Re:It was a design defect (Score:2)
It does not surprise me at all that there are better algorithms out there or that Alder-32 failed, but the failure probability is compound. It only has to work a few times a year in many cases, and Adler-32 *is* used in some respectable systems as the error trap of last resort. Out of curiosity, not being a topical expert, what would be the best CRC algorithm to use on modern silicon? It is also worth noting that some places are starting to use cryptographic hashes instead of CRC for software checksum purposes, so perhaps this is all moot.
Re:It was a design defect (Score:2)
Re:It was a design defect (Score:2)
For those not familiar with checksums, the "ideal" checksum algorithm will toggle approximately 50% of the bits in the checksum for any one bit in the source material toggled. This makes it highly unlikely for several errors in an otherwise correct message to combine to produce the same checksum. Ideally, two messages that produce the same checksum should be wildly different, not nearly identical.
Re:It was a design defect (Score:2)
I agree with you,
particularly with consumer hardware which has many internal paths with no checksums at all.
but, are there any hardware checksums AT ALL in the Intel PC architecture, aside from add-on cards such as HBAs which only protect external data?
PCIe, and ECC ram at least do some kind of error correction, what, two and one bits worth respectively? I think that's it.
This is one of the biggest differences between cheapo Intel hardware and proprietary stuff from Sun, Fujitsu, IBM, HP, etc.
I can't really feel sorry for people who saved a few bucks implementing critical systems on cheap hardware and didn't bother implementing the proper levels of software error correction. They got what they paid for.
Re:It was a design defect (Score:2)
You are correct, Intel processors and chipsets have limited CRC in the internal pathways. In fact, if this matters to you, it is one of the areas where AMDs silicon is better, having more comprehensive error detection. HyperTransport, for example, has CRC.
Re:It was a design defect (Score:2)
This sort of knowledge gap exists in many arenas. A classic error in client-server software: never trust the client. So many "hacks" in online games boil down to the game server trusting the game client to obey the rules, when it's really the server's responsibility to handle all the rule enforcement.
So, yes, software developers as a group frequently fail to learn from those who came before them. In part, this probably has to do with existing education -- it seems like most college programs are always years behind the curve. There's also seems to be a large disconnect between the academic community and the rest; scientists can keep up to date on progress in the field reading academic journals and the like. Programmers, on the other hand, seem to disappear into corporations after college, where much of their knowledge becomes proprietary.
The lack of efficient knowledge sharing in our field is causing us to repeat the same mistakes for decades on end.
Re:It was a design defect (Score:2)
This sort of knowledge gap exists in many arenas. A classic error in client-server software: never trust the client. So many "hacks" in online games boil down to the game server trusting the game client to obey the rules, when it's really the server's responsibility to handle all the rule enforcement.
Unfortunately for a game to be popular it needs to be responsive. Often that means the client doing some of the movement and hit calculations and then the server adjusting those to keep the world somewhat in sync rather than the game doing all the calculations.
And of course it would be crazy to do all the rendering on the server so the client ends of
OTOH more serious software certainly should not be trusting clients without a very good reason.
Re:It was a design defect (Score:1)
Modern games have rather a lot of rules, enough that it's inefficient to have the server run all of them.
It's not a knowledge gap - everyone knows it already - it's a compromise for performance in a field (unlike online shopping) where performance > security.
It was the flood of disgruntled me.com users... (Score:1)
heading for s3.
It providers a timeline of events (Score:1, Funny)
It provideRS? PROVIDERS?!?
I'TS PROVIDED!
S3 (Score:1)
Always happens on a Sunday (Score:2, Interesting)
Re:Always happens on a Sunday (Score:4, Informative)
After working in a production environment as a developer, I can assure you that the correct interpretation is "Anybody else noticed that these major problems always occur when no one is around to catch them (before they get out of hand)?"
InnerWeb
Re:Always happens on a Sunday (Score:2)
Thats funny, I did not catch that double meaning. It was a production environment. Document production, and I was one of the developers who wrote software to keep it going along. So, I developed in a production environment.
InnerWeb
Byzantine failure (Score:3, Interesting)
So the whole cloud is in trouble if one node starts spewing nonsense? So much for redundancy. Amazon developers would be well advised to read up on the "Byzantine Generals" problem.
Re:Byzantine failure (Score:2)
Yeah, they should have bought a book on it from half.com or something.
A customer's reponse (Score:2)
Because we're in Seattle and a few blocks from Amazon's headquarters, we got a personal visit last week from one of the senior managers of Amazon's hosted platforms group. In addition to being able to ask him all kinds of great questions about how they do their business and what technologies they employ that we could also use, we got to ask him about what happened.
He was completely open and honest about it. He knew that we, like every other Amazon S3 customer, had suffered and that some of us had lost a Sunday to dealing with customer complaints. He apologized and told us that they were taking steps to make sure it wouldn't happen again.
Amazon has handled this very well and we will continue to be a customer of theirs.
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Five nines allows for over eight hours of downtime a year.
Gossip protocol decoded (Score:1)
"The server is down, purple monkey dishwasher"