Are you sure about that? Our latest tests show that loosing the drive in a jbod setup makes the broker fail (unfortunately). On Apr 18, 2014 9:01 PM, "Bello, Bob" <bob.be...@dish.com> wrote:
> Yes you would lose the topic/partitions on the drive. I'm not quite sure > if Kafka can determine what topics/partitions are missing or not. I suggest > you try testing it. > > > - Bob > > > -----Original Message----- > From: Andrew Otto [mailto:ao...@wikimedia.org] > Sent: Friday, April 18, 2014 8:36 AM > To: users@kafka.apache.org > Subject: Re: Cluster design distribution and JBOD vs RAID > > > BOB> We are using RAID10. It was a requirement from our Unix guys. The > rationale for this was we didn't want to lose just a disk and to have to > rebuild/re-replicate 20TB of data. We haven't experienced any drive > failures that I am aware of. We have had complete server failures, but the > data was still good. I believe we have 10-4TB drives in a RAID10 > configuration. I/O performance is very good. > > Just curious, would losing one disk in a JBOD setup really mean you'd have > to > re-replicate 20TB of data? If a single drive dies, wouldn't you only lose > the partitions that happen to be on that drive? > > > > > On Apr 17, 2014, at 8:00 PM, Bello, Bob <bob.be...@dish.com> wrote: > > > Some feedback from your feedback. > > > > BERT> We have several uses cases we are looking at kafka for. Today we > are > > just using the file system to buffer data between our systems. We are > > looking at uses cases that have varying message sizes of 200, 300, 1000, > > 2200 bytes > > > > BOB> Since you are using small message size, watch out or large index > files. You can stuff a lot of messages in to the default log file size of > 512MB. We use 1GB log files before rolling them. > > > > > > BERT> The use case we are looking at currently has hourly peaks of about > > 450K messages per second. For sizing we want to make sure we can support > > 900K . Our larger feed in terms of size peaks at 450MBsec so we want to > > make sure the cluster we build can support 900MBsec > > > > BOB> I believe LinkedIn has reported getting a throughput of 900k > messages though a 6 node cluster. If you can achieve a flush rate of > 100MB/s (which is easy for a good RAID setup) having a 12 node cluster > should be doable. Remember when your topic/partition leadership is balance > across the cluster (preferred replica election) you get to take advantage > of all the brokers. Don't forget to architect for a failures. Can your > cluster handle max throughput with two Kafka broker in an offline state? > > > > BERT> Are you implying that the number of topics has direct correlation > to > > the fail-over time? I think I might test this by creating one topic > > loading 500 million rows and test failover and compare to 500 topics > with 1 > > million rows each. Not sure if data in the Q impacts the failover so > > figured I would test that also. > > > > BOB> Yes, that is what we have seen. The current controller architecture > takes longer for Kafka nodes to fail over. It's not the # of topics, but > the # of topic/partitions that have to move over. When a Kafka broker fails > (planed or unplanned), the producers and the consumers have to pause for > all the topic/partition pairs that were the leader for the off line Kafka > broker and they have to move to another Kafka broker that is in ISR. By > having lots of topics/partitions (we have many thousands), it can take a > bit. Remember it's only a chunk, not all topics and partitions. This of > course can change as the Kafka development team changes how this works. I > highly recommend creating your topic and partition counts in DEV/QA and > test this out. You will see a difference. > > > > As for the amout of data in the topic/partition that is of no concern > for failover. The Kafka broker will only failover those topics/partitions > that are in ISR. Replication time once a Kafka broker is brought back > online will depend on how far behind the Kafka broker is from the leader. > This is delta in the offset. Planned shutdowns can be minutes, unplanned > shutdowns/failures can take hours for our data to re-replicate. > > > > > > BERT> Our default config config has a 256GB of memory also. One thing I > > do want to test is impact on cluster of reading data not in memory. Have > > you done any testing like this? > > > > BOB> Yes, it's about putting enough data to flush outside the OS file > cache. But 512GB of data in your topics to make sure the data is not in the > cache. Also, you can reset and/or use new consumer groups and make sure you > read from the lowest-offset. Watch your iostats to see if you get lots of > reads. On a normal Kafka cluster that is reading cached memory (for > consumption), you will not see read IO. Assuming you don't have other > processes on the system reading data (such as log aggregation). We see 30MB > writes/flushes ever-other-second with 1-2% IO utilization. > > > > > > BERT> We have not determined what to use just yet for monitoring. What > > are you guys using? > > > > BOB> We are using a commercial APM solution. It's an java agent the > plugs into the JVM on boot time. This reads the JMX information as well as > file I/O rates, NIO rates and GC. It sends to a centralized monitoring > console. Google "Java APM" for some ideas. > > > > > > BERT> Can you share more about your config? Are you using RAID10 or > > RAID5? What size and speed of drives? Have you needed to do a RAID > > rebuild and if so did it negatively impact the cluster. The standard > > server I was given has 12 x 4TB 7.2K drives. I will either run in JBOD > or > > as RAID10. Parity based RAID with 4TB drives makes me nervous. I am not > > worried about performance when things are working as designed...we need > to > > plan for edge cases when consumer is reading old data or the system needs > > to play catch up on a big backlog. > > > > BOB> We are using RAID10. It was a requirement from our Unix guys. The > rationale for this was we didn't want to lose just a disk and to have to > rebuild/re-replicate 20TB of data. We haven't experienced any drive > failures that I am aware of. We have had complete server failures, but the > data was still good. I believe we have 10-4TB drives in a RAID10 > configuration. I/O performance is very good. > > > > BERT> Need to spend some time on zookeeper. I have not looked at > > zookeeper performance to see if its negatively impacting the performance > > tests I am doing. We haven't spent any time looking at zookeeper. Did > you > > find that the SSD helped improve kafka performance? > > > > BOB> We started with SSD. Kafka brokers itself doesn't write a lot of > data frequently (to zookeeper). It's really about how your consumers flush > their offsets. This is assuming you will be using the high-level consumer > client. If you are going to flush the offsets to zookeeper on every message > consumed (to get best effort nearly-exactly-once processing). You will > being writing a lot of data to zookeeper. On our 5 node zookeeper cluster, > we are doing 300+ writes per second, and can spike up to many 1000's. > Typically it's 1-2MBs data rate. The SSDs are under 2% I/O utilization. > 200MB of ZK data, and we clean up the files once per hour. We run some > consumers in batch and flush on time delay. Other consumers are flush per > message processed. It's the flush per message that causes the high-volume. > > > > Push back on DEVs and software architecture if they want to flush per > message. Do it where it's only absolutely necessary. :) > > > > The high level Kafka consumer is good at "at least once" processing. > Exactly once is a harder nut to crack. Exactly once processing may require > some custom code around the low-level Kafka consumer client. > > > > - Bob > > > > > > > > -----Original Message----- > > From: bertc...@gmail.com [mailto:bertc...@gmail.com] On Behalf Of Bert > Corderman > > Sent: Thursday, April 17, 2014 7:21 AM > > To: users@kafka.apache.org > > Subject: Re: Cluster design distribution and JBOD vs RAID > > > > Hey Bob, > > > > thanks for your detailed response. I have added comments inline. > > > > > > On Wed, Apr 16, 2014 at 7:41 PM, Bello, Bob <bob.be...@dish.com> wrote: > > > >> Perhaps as you consider the size of your cluster, a few questions about > >> the kind of messaging you are looking at? I can use an example of what > we > >> do in our production environment while not going into specifics. These > are > >> just observations from an OPS perspective. (sorry for the wall of text.) > >> > >> * Size of messages (<100 bytes, <1kB, <10kB, <100kB, <1MB, <10MB, etc). > >> (we run messages size between a few byes to over 100KB with a few at > over > >> 1MB). > >> > > BERT> We have several uses cases we are looking at kafka for. Today we > are > > just using the file system to buffer data between our systems. We are > > looking at uses cases that have varying message sizes of 200, 300, 1000, > > 2200 bytes > > > >> > >> * Volume of messages per second (we produce over 15k per second and can > >> consume over 100K per second when we are processing though some lag) > >> > > BERT> The use case we are looking at currently has hourly peaks of about > > 450K messages per second. For sizing we want to make sure we can support > > 900K . Our larger feed in terms of size peaks at 450MBsec so we want to > > make sure the cluster we build can support 900MBsec > > > >> > >> * # of Producer clients (a few, a lot) (we have over 300 app servers the > >> produce messages to the Kafka cluster) > >> ** Not only does this affect Kafka broker performance but it can use a > lot > >> of TCP connections specially if you run a large Kafka cluster > >> > > BERT> our producer count will be low ...maybe 8-16 hosts. > > > >> > >> * # of Consumer clients (a few, a lot) (we have less than 50 app servers > >> that consume at this time) > >> ** This also affects the # of TCP connections to Kafka brokers. (We have > >> over 2400+ TCP connections to our cluster) > >> > > BERT> This will be much higher but not sure yet. We are also looking at > > replacing some legacy technology with storm so this is a bit up in the > air > > right now. > > > >> > >> * Will you compress your message before sending them to Kafka? (we have > a > >> mix of snappy, gzip and non-compressed messages depending on the > >> application). This can affect your disk usage > >> > > BERT> We will use whatever performs best ;) My gut is that we will be > > using snappy > > > >> > >> * Planned retention period. Longer retention period = more storage > >> required. (we have varied retention periods per topic, between 10 days > and > >> 30 days). > >> > >> * The number of topics per cluster. I believe Kafka scales well with the > >> number of topics, however you have to worry about a few things: > >> ** More topics, means slower migration/failover when Kafka brokers are > >> shutdown or fail. This has caused us time out issues. Planned shutdown > of a > >> Kafka broker can take over 30 seconds to over 3 minutes. (We have over > >10 > >> and <50 topics. We are growing topics rapidly.) > >> > > BERT> Are you implying that the number of topics has direct correlation > to > > the fail-over time? I think I might test this by creating one topic > > loading 500 million rows and test failover adn compare to 500 topics > with 1 > > million rows each. Not sure if data in the Q impacts the failover so > > figured I would test that also. > > > >> > >> * The number of partitions per topic. More partitions per topic = more > >> open file handles, (2 per log file, one for data and one more the > index). > >> We run average of 130 partitions. You have to consider your cardinality > for > >> your messages if order is important. Can you use a key that allows a > good > >> distribution across partitions while maintaining order? If all your > message > >> end up in just a few partitions within the topic then it's harder scale > the > >> consumption. This all depends on your use case. > >> > > BERT> We are lucky that order is not critical for our large feeds. > > > >> > >> It might sound like good rationale to scale the # of partitions for a > >> topic to a huge number (for just in case). I think it all depends. > >> > >> * How many consumer threads can consume a single topic? You can't go > wider > >> than the # of partitions however Kafka clients easily work with a large > # > >> of partitions with a few consumer threads. > >> > >> * Producer vs. Consumer size. Is your messaging flow Producer or > Consumer > >> heavy. Kafka is awesome and sending data to consumers that use "recent" > >> data. Since Kafka uses memory mapped files, any data from Kafka that is > in > >> RAM will be very fast. (Our servers have 256GB of ram on them). > >> > > BERT> Our default config config has a 256GB of memory also. One thing I > > do want to test is impact on cluster of reading data not in memory. Have > > you done any testing like this? > > > >> > >> * Size of your cluster vs. the # of replicas. Larger # of Kafka brokers > >> means more chance of failure within the cluster. Same kind of reason why > >> you generally won't see a large RAID5 array. You get one failure before > you > >> lose data. If you decide to run a large cluster and # of replicas will > be > >> important. How much risk are you willing to take? (We run a 6 node > cluster > >> with a replica factor of 3. We can lose a total of two nodes before > losing > >> data). > >> > > BERT> Thanks for the datapoint. We were also planning to go with > > replication factor of 3 > > > >> > >> * Are you running on native iron or virtualized? VM is generally lower > >> performance but can generally spin up new instances faster upon > failure. We > >> run on native iron so we get excellent performance at the cost of longer > >> lead times to provision new Kafka brokers. > >> > > BERT> We are big fans of vms...however kafka will be on physical > > > >> > >> * Networking. Are you are running 100mbit, 1gig or 10gib? You can only > >> produce and consume so much data. Larger clusters let you run a total > >> aggregate bandwidth. Don't forget about replication! Topic/partition > >> leaders must replicate to all replica Kafkabrokers (hub/spoke). How long > >> can you wait for replication to occur after a planned or un-planned > outage? > >> (We run >1Gig). > >> > > BERT> 10gb....so cheap now. I did cost analysis and found that a single > > 10gb port costs about the same as 2 x 1gig. Five times the bandwidth and > > less latency makes it no brainer. If your kafka hosts have multiple nics > > make sure they are using the right port. This one bit me for a little. > > (hostname config in the broker config) > > > >> > >> * Monitoring. Large # of Kafka brokers means more to monitor. Do you > have > >> a centralized monitoring app? Kafka provides a lot (huge!) JMX > information. > >> Making sense of it all can take some time. > >> > > BERT> We have not determined what to use just yet for monitoring. What > > are you guys using? > > > > > >> * Disk I/O. JBOD vs. RAID. How much are you willing to tolerate > failures? > >> Do you have provisioned IO? (We run native iron and local disk in a RAID > >> configuration. It was easier for us to manage a single mount point than > a > >> bunch in a JBOD configuration. We rely of local RAID and Kafka > replication > >> to keep enough copies of our data. We have a large amount of disk > capacity. > >> We can tolerate large re-replication events due to broker failure > without > >> affecting producer or consumer performance.) > >> > > BERT> Can you share more about your config? Are you using RAID10 or > > RAID5? What size and speed of drives? Have you needed to do a RAID > > rebuild and if so did it negatively impact the cluster. The standard > > server I was given has 12 x 4TB 7.2K drives. I will either run in JBOD > or > > as RAID10. Parity based RAID with 4TB drives makes me nervous. I am not > > worried about performance when things are working as designed...we need > to > > plan for edge cases when consumer is reading old data or the system needs > > to play catch up on a big backlog. > > > >> > >> * Disk capacity / Kafka Broker capacity. Depending on your volume, > message > >> size and retention period, how much disk space will you need? (Using our > >> "crystal ball tech(tm)" we decided over 20TB per Kafka broker would meet > >> our needs. We will probably add Kafka brokers over adding disk as we > >> outgrow this.) > >> > > BERT> I need a crystal ball ;) > > > >> > >> * Separate clusters to keep information separated? Do you have a use > case > >> for keeping customer data separate? Compliance use cases such as PCI or > >> SOX? This may be a good reason to keep separate Kafka clusters. I assume > >> that you already will keep separate clusters for DEV/QA/PROD. > >> > > BERT> yes DEV/QA/PROD completely separate > > > >> > >> * Zookeeper performance - 3 node, 5 node or 7 node. Less nodes, better > >> performance. More nodes, better failure tolerance. We run 5 nodes with > the > >> transaction logs on SSD. Our ZK update performance is very good. > >> > > BERT> Need to spend some time on zookeeper. I have not looked at > > zookeeper performance to see if its negatively impacting the performance > > tests I am doing. We haven't spent any time looking at zookeeper. Did > you > > find that the SSD helped improve kafka performance? > > > >> > >> # of partitions per Topic debate: > >> Personally, I'm a proponent of larger # of partitions per topic without > >> going way large. You can add Kafka Brokers to increase capacity and get > >> more performance. However though it's possible to add partitions after a > >> topic is created, it can cause issues with your key hashing depending on > >> your message architecture. > >> > >> * Increasing # of brokers = easy > >> * Increasing the # of partitions in a topic with data in it = hard > >> > >> For us, we will be adding more topics and as we add additional messaging > >> functionality. > >> > >> Example: > >> > >> 130 partitions per topic / 6 brokers = 5 leader partitions per broker > per > >> topic. If you replicate 3 the you will end up with 3x active partitions > per > >> broker. > >> > >> 1024 partitions per topic / 24 brokers =~ 43 leader partitions per > broker > >> per topic. > >> > > BERT> Thanks for the example. Good to see others are using larger > > partition counts. > > > >> > >> > >> Final thoughts: > >> > >> There's no magical formula for this as already stated in the wiki. It > is a > >> lot of trial and error. I will say that we went from a few 100 messages > per > >> second volume to over 40k per second by adding one application and our > >> Kafka cluster didn't even blink. > >> > >> Kafka is awesome. > >> > >> Btw, we're running 0.8.0. > >> > >> > >> > >> - Bob > >> > >> -----Original Message----- > >> From: bertc...@gmail.com [mailto:bertc...@gmail.com] On Behalf Of Bert > >> Corderman > >> Sent: Wednesday, April 16, 2014 11:58 AM > >> To: users@kafka.apache.org > >> Subject: Cluster design distribution and JBOD vs RAID > >> > >> I am wondering what others are doing in terms of cluster separation. > (if at > >> all) For example let's say I need 24 nodes to support a given workload. > >> What are the tradeoffs between a single 24 node cluster vs 2 x 12 node > >> clusters for example. The application I support can support separation > of > >> data fairly easily as the data is all processed in the same way but can > be > >> sharded isolated based on customers. I understand the standard > tradeoffs, > >> for example putting all your eggs in one basket but curious as if there > are > >> any details specific to Kafka in terms of cluster scale out. > >> > >> > >> > >> Somewhat related is the use of RAID vs JBOD, I have reviewed the > documents > >> on the Kafka site and understand the tradeoff between space as well as > >> sequential IO vs random and the fact a RAID rebuild might kill the > system. > >> I am specifically asking the question as it relates to larger cluster > and > >> the impact on the number of partitions a topic might need. > >> > >> > >> > >> Take an example of a 24 node cluster with 12 drives each the cluster > would > >> have 288 drives. To ensure a topic is distributed across all drives a > >> topic would require 288 partitions. I am planning to test some of this > but > >> wanted to know if there was a rule of thumb. The following link > >> > >> > https://cwiki.apache.org/confluence/display/KAFKA/FAQ#FAQ-HowdoIchoosethenumberofpartitionsforatopic > >> ? > >> Talks about supporting up to 10K partitions but its not clear if this is > >> for a cluster as a whole vs topic based > >> > >> > >> Those of you running larger clusters what are you doing? > >> > >> > >> Bert > >> > >
