Hey Chris, Thanks for sharing all the info. I have few questions: 1. What are you doing with so much memory :) ? How much of it do you allocate for heap ? 2. What your network speed ? Do you use trunks ? Do you have a dedicated VLAN for gossip/store traffic ?
Cheers, Sorin On Sun, Oct 30, 2011 at 5:00 AM, Chris Goffinet <c...@chrisgoffinet.com>wrote: > RE: RAID0 Recommendation > > Cassandra supports multiple data file directories. Because we do > compactions, it's just much easier to deal with (1) data file directory > that is stripped across all disks as 1 volume (RAID0). There are other ways > to accomplish this though. At Twitter we use software raid (RAID0 & RAID10). > > We own the physical hardware and have found that even with hardware raid, > software raid in Linux actually faster. The reason being is: > > http://en.wikipedia.org/wiki/Non-standard_RAID_levels#Linux_MD_RAID_10 > > We have found that using far-copies is much faster over near-copies. We > set the i/o scheduler to noop at the moment. We might move back to CFQ with > more tuning in the future. > > We use RAID10 for cases where we need better disk performance if we are > hitting the disk often, sacrificing storage. We initially thought RAID0 > should be faster over RAID10 until we found out about the near vs far > layouts. > > RE: Hardware > > This is going to depend on how well your automated infrastructure is, but > we chose the path of finding the cheapest servers we could get from > Dell/HP/etc. 8/12 cores, 72gb memory per node, 2TB/3TB, 2.5". > > We are in the process of making changes to our servers, I'll report back > in when we have more details to share. > > I wouldn't recommend 75 CFs. It could work but just seems too complex. > > Another recommendation for clusters, always go big. You will be thankful > in the future for this. Even if you can do this on 3-6 nodes, go much > larger for future expansion. If you own your hardware and racks, I > recommend making sure to size out the rack diversity and # of nodes per > rack. Also take into account the replication factor when doing this. RF=3, > should be min of 3 racks, and # of nodes per rack should be divisible by > the replication factor. This has worked out pretty well for us. Our biggest > problems today are adding 100s of nodes to existing clusters at once. I'm > not sure how many other companies are having this problem, but it's > certainly on our radar to improve, if you get to that point :) > > > On Tue, Oct 25, 2011 at 5:23 AM, Alexandru Sicoe <adsi...@gmail.com>wrote: > >> Hi everyone, >> >> I am currently in the process of writing a hardware proposal for a >> Cassandra cluster for storing a lot of monitoring time series data. My >> workload is write intensive and my data set is extremely varied in types of >> variables and insertion rate for these variables (I will have to handle an >> order of 2 million variables coming in, each at very different rates - the >> majority of them will come at very low rates but there are many that will >> come at higher rates constant rates and a few coming in with huge spikes in >> rates). These variables correspond to all basic C++ types and arrays of >> these types. The highest insertion rates are received for basic types, out >> of which U32 variables seem to be the most prevalent (e.g. I recorded 2 >> million U32 vars were inserted in 8 mins of operation while 600.000 doubles >> and 170.000 strings were inserted during the same time. Note this >> measurement was only for a subset of the total data currently taken in). >> >> At the moment I am partitioning the data in Cassandra in 75 CFs (each CF >> corresponds to a logical partitioning of the set of variables mentioned >> before - but this partitioning is not related with the amount of data or >> rates...it is somewhat random). These 75 CFs account for ~1 million of the >> variables I need to store. I have a 3 node Cassandra 0.8.5 cluster (each >> node is a 4 real core with 4 GB RAM and split commit log directory and data >> file directory between two RAID arrays with HDDs). I can handle the load in >> this configuration but the average CPU usage of the Cassandra nodes is >> slightly above 50%. As I will need to add 12 more CFs (corresponding to >> another ~ 1 million variables) plus potentially other data later, it is >> clear that I need better hardware (also for the retrieval part). >> >> I am looking at Dell servers (Power Edge etc) >> >> Questions: >> >> 1. Is anyone using Dell HW for their Cassandra clusters? How do they >> behave? Anybody care to share their configurations or tips for buying, what >> to avoid etc? >> >> 2. Obviously I am going to keep to the advice on the >> http://wiki.apache.org/cassandra/CassandraHardware and split the >> commmitlog and data on separate disks. I was going to use SSD for commitlog >> but then did some more research and found out that it doesn't make sense to >> use SSDs for sequential appends because it won't have a performance >> advantage with respect to rotational media. So I am going to use rotational >> disk for the commit log and an SSD for data. Does this make sense? >> >> 3. What's the best way to find out how big my commitlog disk and my data >> disk has to be? The Cassandra hardware page says the Commitlog disk >> shouldn't be big but still I need to choose a size! >> >> 4. I also noticed RAID 0 configuration is recommended for the data file >> directory. Can anyone explain why? >> >> Sorry for the huge email..... >> >> Cheers, >> Alex >> > >
