Oh, my bad. There was a flood of information there, I didn't realize you had switched to two DCs. It's been a long day.
I'll be honest, it's really hard to read your various options as you've intermixed terminology from AWS and Cassandra in a weird way and there's several pages of information here to go through. I don't have time to decipher it, sorry. Spread a DC across 3 AZs if you want to be fault tolerant and will use RF=3, use a single AZ if you don't care about full DC failure in the case of an AZ failure or you're not using RF=3. On Wed, Oct 23, 2019 at 4:56 PM Sergio <lapostadiser...@gmail.com> wrote: > OPTION C or OPTION A? > > Which one are you referring to? > > Both have separate DCs to keep the workload separate. > > - OPTION A) > - Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1a > - 3 read ONE us-east-1a > - 4 write TWO us-east-1b 5 write TWO us-east-1b > - 6 write TWO us-east-1b > > > Here we have 2 DC read and write > One Rack per DC > One Availability Zone per DC > > Thanks, > > Sergio > > > On Wed, Oct 23, 2019, 1:11 PM Jon Haddad <j...@jonhaddad.com> wrote: > >> Personally, I wouldn't ever do this. I recommend separate DCs if you >> want to keep workloads separate. >> >> On Wed, Oct 23, 2019 at 4:06 PM Sergio <lapostadiser...@gmail.com> wrote: >> >>> I forgot to comment for >>> >>> OPTION C) >>> 1. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1b >>> 2. 3 read ONE us-east-1c >>> 3. 4 write TWO us-east-1a 5 write TWO us-east-1b >>> 4. 6 write TWO us-east-1c I would expect that I need to decrease the >>> Consistency Level in the reads if one of the AZ goes down. Please >>> consider >>> the below one as the real OPTION A. The previous one looks to be wrong >>> because the same rack is assigned to 2 different DC. >>> 5. OPTION A) >>> 6. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1a >>> 7. 3 read ONE us-east-1a >>> 8. 4 write TWO us-east-1b 5 write TWO us-east-1b >>> 9. 6 write TWO us-east-1b >>> >>> >>> >>> Thanks, >>> >>> Sergio >>> >>> Il giorno mer 23 ott 2019 alle ore 12:33 Sergio < >>> lapostadiser...@gmail.com> ha scritto: >>> >>>> Hi Reid, >>>> >>>> Thank you very much for clearing these concepts for me. >>>> https://community.datastax.com/comments/1133/view.html I posted this >>>> question on the datastax forum regarding our cluster that it is unbalanced >>>> and the reply was related that the *number of racks should be a >>>> multiplier of the replication factor *in order to be balanced or 1. I >>>> thought then if I have 3 availability zones I should have 3 racks for each >>>> datacenter and not 2 (us-east-1b, us-east-1a) as I have right now or in the >>>> easiest way, I should have a rack for each datacenter. >>>> >>>> >>>> >>>> 1. Datacenter: live >>>> ================ >>>> Status=Up/Down >>>> |/ State=Normal/Leaving/Joining/Moving >>>> -- Address Load Tokens Owns Host ID >>>> Rack >>>> UN 10.1.20.49 289.75 GiB 256 ? >>>> be5a0193-56e7-4d42-8cc8-5d2141ab4872 us-east-1a >>>> UN 10.1.30.112 103.03 GiB 256 ? >>>> e5108a8e-cc2f-4914-a86e-fccf770e3f0f us-east-1b >>>> UN 10.1.19.163 129.61 GiB 256 ? >>>> 3c2efdda-8dd4-4f08-b991-9aff062a5388 us-east-1a >>>> UN 10.1.26.181 145.28 GiB 256 ? >>>> 0a8f07ba-a129-42b0-b73a-df649bd076ef us-east-1b >>>> UN 10.1.17.213 149.04 GiB 256 ? >>>> 71563e86-b2ae-4d2c-91c5-49aa08386f67 us-east-1a >>>> DN 10.1.19.198 52.41 GiB 256 ? >>>> 613b43c0-0688-4b86-994c-dc772b6fb8d2 us-east-1b >>>> UN 10.1.31.60 195.17 GiB 256 ? >>>> 3647fcca-688a-4851-ab15-df36819910f4 us-east-1b >>>> UN 10.1.25.206 100.67 GiB 256 ? >>>> f43532ad-7d2e-4480-a9ce-2529b47f823d us-east-1b >>>> So each rack label right now matches the availability zone and we >>>> have 3 Datacenters and 2 Availability Zone with 2 racks per DC but the >>>> above is clearly unbalanced >>>> If I have a keyspace with a replication factor = 3 and I want to >>>> minimize the number of nodes to scale up and down the cluster and keep >>>> it >>>> balanced should I consider an approach like OPTION A) >>>> 2. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1a >>>> 3. 3 read ONE us-east-1a >>>> 4. 4 write ONE us-east-1b 5 write ONE us-east-1b >>>> 5. 6 write ONE us-east-1b >>>> 6. OPTION B) >>>> 7. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1a >>>> 8. 3 read ONE us-east-1a >>>> 9. 4 write TWO us-east-1b 5 write TWO us-east-1b >>>> 10. 6 write TWO us-east-1b >>>> 11. *7 read ONE us-east-1c 8 write TWO us-east-1c* >>>> 12. *9 read ONE us-east-1c* Option B looks to be unbalanced and I >>>> would exclude it OPTION C) >>>> 13. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1b >>>> 14. 3 read ONE us-east-1c >>>> 15. 4 write TWO us-east-1a 5 write TWO us-east-1b >>>> 16. 6 write TWO us-east-1c >>>> 17. >>>> >>>> >>>> so I am thinking of A if I have the restriction of 2 AZ but I guess >>>> that option C would be the best. If I have to add another DC for reads >>>> because we want to assign a new DC for each new microservice it would >>>> look >>>> like: >>>> OPTION EXTRA DC For Reads >>>> 1. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1b >>>> 2. 3 read ONE us-east-1c >>>> 3. 4 write TWO us-east-1a 5 write TWO us-east-1b >>>> 4. 6 write TWO us-east-1c 7 extra-read THREE us-east-1a >>>> 5. 8 extra-read THREE us-east-1b >>>> 6. >>>> 7. >>>> >>>> >>>> 1. 9 extra-read THREE us-east-1c >>>> 2. >>>> The DC for *write* will replicate the data in the other >>>> datacenters. My scope is to keep the *read* machines dedicated to >>>> serve reads and *write* machines to serve writes. Cassandra will >>>> handle the replication for me. Is there any other option that is I >>>> missing >>>> or wrong assumption? I am thinking that I will write a blog post about >>>> all >>>> my learnings so far, thank you very much for the replies Best, Sergio >>>> >>>> >>>> Il giorno mer 23 ott 2019 alle ore 10:57 Reid Pinchback < >>>> rpinchb...@tripadvisor.com> ha scritto: >>>> >>>>> No, that’s not correct. The point of racks is to help you distribute >>>>> the replicas, not further-replicate the replicas. Data centers are what >>>>> do >>>>> the latter. So for example, if you wanted to be able to ensure that you >>>>> always had quorum if an AZ went down, then you could have two DCs where >>>>> one >>>>> was in each AZ, and use one rack in each DC. In your situation I think >>>>> I’d >>>>> be more tempted to consider that. Then if an AZ went away, you could fail >>>>> over your traffic to the remaining DC and still be perfectly fine. >>>>> >>>>> >>>>> >>>>> For background on replicas vs racks, I believe the information you >>>>> want is under the heading ‘NetworkTopologyStrategy’ at: >>>>> >>>>> http://cassandra.apache.org/doc/latest/architecture/dynamo.html >>>>> >>>>> >>>>> >>>>> That should help you better understand how replicas distribute. >>>>> >>>>> >>>>> >>>>> As mentioned before, while you can choose to do the reads in one DC, >>>>> except for concerns about contention related to network traffic and >>>>> connection handling, you can’t isolate reads from writes. You can _ >>>>> *mostly*_ insulate the write DC from the activity within the read DC, >>>>> and even that isn’t an absolute because of repairs. However, your mileage >>>>> may vary, so do what makes sense for your usage pattern. >>>>> >>>>> >>>>> >>>>> R >>>>> >>>>> >>>>> >>>>> *From: *Sergio <lapostadiser...@gmail.com> >>>>> *Reply-To: *"user@cassandra.apache.org" <user@cassandra.apache.org> >>>>> *Date: *Wednesday, October 23, 2019 at 12:50 PM >>>>> *To: *"user@cassandra.apache.org" <user@cassandra.apache.org> >>>>> *Subject: *Re: Cassandra Rack - Datacenter Load Balancing relations >>>>> >>>>> >>>>> >>>>> *Message from External Sender* >>>>> >>>>> Hi Reid, >>>>> >>>>> Thanks for your reply. I really appreciate your explanation. >>>>> >>>>> We are in AWS and we are using right now 2 Availability Zone and not >>>>> 3. We found our cluster really unbalanced because the keyspace has a >>>>> replication factor = 3 and the number of racks is 2 with 2 datacenters. >>>>> We want the writes spread across all the nodes but we wanted the reads >>>>> isolated from the writes to keep the load on that node low and to be able >>>>> to identify problems in the consumers (reads) or producers (writes) >>>>> applications. >>>>> It looks like that each rack contains an entire copy of the data so >>>>> this would lead to replicate for each rack and then for each node the >>>>> information. If I am correct if we have a keyspace with 100GB and >>>>> Replication Factor = 3 and RACKS = 3 => 100 * 3 * 3 = 900GB >>>>> If I had only one rack across 2 or even 3 availability zone I would >>>>> save in space and I would have 300GB only. Please correct me if I am >>>>> wrong. >>>>> >>>>> Best, >>>>> >>>>> Sergio >>>>> >>>>> >>>>> >>>>> Il giorno mer 23 ott 2019 alle ore 09:21 Reid Pinchback < >>>>> rpinchb...@tripadvisor.com> ha scritto: >>>>> >>>>> Datacenters and racks are different concepts. While they don't have >>>>> to be associated with their historical meanings, the historical meanings >>>>> probably provide a helpful model for understanding what you want from >>>>> them. >>>>> >>>>> When companies own their own physical servers and have them housed >>>>> somewhere, the questions arise on where you want to locate any particular >>>>> server. It's a balancing act on things like network speed of related >>>>> servers being able to talk to each other, versus fault-tolerance of having >>>>> many servers not all exposed to the same risks. >>>>> >>>>> "Same rack" in that physical world tended to mean something like "all >>>>> behind the same network switch and all sharing the same power bus". The >>>>> morning after an electrical glitch fries a power bus and thus everything >>>>> in >>>>> that rack, you realize you wished you didn't have so many of the same type >>>>> of server together. Well, they were servers. Now they are door stops. >>>>> Badness and sadness. >>>>> >>>>> That's kind of the mindset to have in mind with racks in Cassandra. >>>>> It's an artifact for you to separate servers into pools so that the >>>>> disparate pools have hopefully somewhat independent infrastructure risks. >>>>> However, all those servers are still doing the same kind of work, are the >>>>> same version, etc. >>>>> >>>>> Datacenters are amalgams of those racks, and how similar or different >>>>> they are from each other depends on what you want to do with them. What >>>>> is >>>>> true is that if you have N datacenters, each one of them must have enough >>>>> disk storage to house all the data. The actual physical footprint of that >>>>> data in each DC depends on the replication factors in play. >>>>> >>>>> Note that you sorta can't have "one datacenter for writes" because the >>>>> writes will replicate across the data centers. You could definitely >>>>> choose >>>>> to have only one that takes read queries, but best to think of writing as >>>>> being universal. One scenario you can have is where the DC not taking >>>>> live >>>>> traffic read queries is the one you use for maintenance or performance >>>>> testing or version upgrades. >>>>> >>>>> One rack makes your life easier if you don't have a reason for >>>>> multiple racks. It depends on the environment you deploy into and your >>>>> fault tolerance goals. If you were in AWS and wanting to spread risk >>>>> across availability zones, then you would likely have as many racks as AZs >>>>> you choose to be in, because that's really the point of using multiple >>>>> AZs. >>>>> >>>>> R >>>>> >>>>> >>>>> On 10/23/19, 4:06 AM, "Sergio Bilello" <lapostadiser...@gmail.com> >>>>> wrote: >>>>> >>>>> Message from External Sender >>>>> >>>>> Hello guys! >>>>> >>>>> I was reading about >>>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__cassandra.apache.org_doc_latest_architecture_dynamo.html-23networktopologystrategy&d=DwIBaQ&c=9Hv6XPedRSA-5PSECC38X80c1h60_XWA4z1k_R1pROA&r=OIgB3poYhzp3_A7WgD7iBCnsJaYmspOa2okNpf6uqWc&m=xmgs1uQTlmvCtIoGJKHbByZZ6aDFzS5hDQzChDPCfFA&s=9ZDWAK6pstkCQfdbwLNsB-ZGsK64RwXSXfAkOWtmkq4&e= >>>>> >>>>> I would like to understand a concept related to the node load >>>>> balancing. >>>>> >>>>> I know that Jon recommends Vnodes = 4 but right now I found a >>>>> cluster with vnodes = 256 replication factor = 3 and 2 racks. This is >>>>> unbalanced because the racks are not a multiplier of the replication >>>>> factor. >>>>> >>>>> However, my plan is to move all the nodes in a single rack to >>>>> eventually scale up and down the node in the cluster once at the time. >>>>> >>>>> If I had 3 racks and I would like to keep the things balanced I >>>>> should scale up 3 nodes at the time one for each rack. >>>>> >>>>> If I would have 3 racks, should I have also 3 different >>>>> datacenters so one datacenter for each rack? >>>>> >>>>> Can I have 2 datacenters and 3 racks? If this is possible one >>>>> datacenter would have more nodes than the others? Could it be a problem? >>>>> >>>>> I am thinking to split my cluster in one datacenter for reads and >>>>> one for writes and keep all the nodes in the same rack so I can scale up >>>>> once node at the time. >>>>> >>>>> >>>>> >>>>> Please correct me if I am wrong >>>>> >>>>> >>>>> >>>>> Thanks, >>>>> >>>>> >>>>> >>>>> Sergio >>>>> >>>>> >>>>> >>>>> >>>>> --------------------------------------------------------------------- >>>>> >>>>> To unsubscribe, e-mail: user-unsubscr...@cassandra.apache.org >>>>> >>>>> For additional commands, e-mail: user-h...@cassandra.apache.org >>>>> >>>>> >>>>> >>>>> >>>>>
