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Christian
thank you so much for your answer. You're right, when I say Performance, I actually mean the "classic FIO test"..... Regarding the CPU, you meant 2Ghz per OSD and per CPU CORE, isn't? One last question, with a total number of 18xOSD (2TB/OSD), and a replica factor of 2, is it really risky? This won't be a critical cluster, but neither is a lab/test cluster, you know.... Thanks again. J > Date: Fri, 2 Oct 2015 17:16:21 +0900 > From: chibi@xxxxxxx > To: ceph-users@xxxxxxxxxxxxxx > CC: magicboiz@xxxxxxxxxxx > Subject: Re: Predict performance > > > Hello, > > More line breaks, formatting. > A wall of text makes people less likely to read things. > > On Fri, 2 Oct 2015 07:08:29 +0000 Javier C.A. wrote: > > > Hello > > Before posting this message, I've been reading older posts in the > > mailing list, but I didn't get any clear answer..... > > Define performance. > Many people seem to be fascinated by the speed of sequential (more or less) > writes and reads, while their use case would actually be better served by > an increased small IOPS performance. > > >I happen to have > > three servers available to test Ceph, and I would like to know if there > > is any kind of "performance prediction formula". > > If there is such a thing (that actually works with less than a 10% error > margin), I'm sure RedHat would like to charge you for it. ^_- > > >-My OSD servers are: > > - 1 x Intel E5-2603v3 1.6Ghz (6 cores) > Slightly underpowered, especially when it comes to small write IOPS. > My personal formula is at least 2GHz per OSD with SSD journal. > > >- 32G RAM D4 > OK, more is better (for read performance, see below). > > >- 10Gb ethernet network, jumbo frames enabled - > > Slight overkill given the rest of your setup, I guess you saw all the fun > people keep having with jumbo frames in the ML archives. > > >SSOO: 2 x 500GB RAID 1 > >- OSD (6 OSD): - 2TB 7200 SATA4 6Gbps > >- 1 x SSD Intel SC3700 200GB for > > journaling of all 6 OSDs. - > This means that the most throughput you'll ever be able to write to those > nodes is the speed of that SSD, 365MB/s, lets make that 350MB/s. > Thus the slight overkill comment earlier. > OTOH the HDDs get to use most of the IOPS (after discounting FS journals, > overhead, the OSD leveldb, etc). > So lets say slightly less than 100 IOPS per OSD. > > >Replication factor = 2. > see below. > > >- XFS > I find Ext4 faster, but that's me. > > >-MON nodes > > will be running in other servers. With this OSD setup, how could I > > predict the cpeh cluster performace (IOPS, R/W BW, latency...)? > > Of these, latency is the trickiest one, as so many things factor into it > aside from the network. > A test case where you're hitting basically just one OSD will look a lot > worse than what an evenly spread out (more threads over a sufficiently > large data set) test would. > > Userspace (librbd) results can/will vastly differ from kernel RBD clients. > > IOPS is a totally worthless data point w/o clearly defining what you're > measuring how. > Lets assume the "standard" of 4KB blocks and 32threads, random writes. > Also lets assume a replication factor of 3, see below. > > Sustained sync'ed (direct=1 option in fio) IOPS with your setup will be in > the 500 to 600 range (given a quiescent cluster). > This of course can change dramatically with non-direct writes and caching > (kernel page cache and/or RBD client caches). > > The same is true for reads, if your data set fits into the page caches of > your storage nodes, it will be fast, if everything needs to be read from > the HDDs, you're back to what these devices can do (~100 IOPS per HDD). > > To give you a concrete example, on my test cluster I have 5 nodes, 4 > HDDs/OSDs each and no journal SSDs. > So that's in theory 100 IOPS per HDD, divided by 2 for the on-disk journal, > divided by 3 for replication: > 20*100/2/3=333 > Which amazingly is what I get with rados bench and 4K blocks, fio from a > kernel client and direct I/O is around 200. > > BW, as in throughput is easier, about 350MB/s max for sustained sequential > writes (the limit of the journal SSD) and lets say 750MB/s for sustained > reads. > Again, if you're reading just 8GB in your tests and that fits nicely in > the page caches of the OSDs, it will be wire speed. > > >Should I configure a replica factor of 3? > > > If you value your data, which you will on a production server, then yes. > This will of course cost you 1/3 of your performance compared to replica 2. > > Regards, > > Christian > -- > Christian Balzer Network/Systems Engineer > chibi@xxxxxxx Global OnLine Japan/Fusion Communications > http://www.gol.com/ |
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