> If each OSD requires 4T Nobody said that. What was said is HDD=1T, SSD=3T. It depends on the drive type!
The %-utilisation information is just from top observed during heavy load. It does not show how the kernel schedules things on physical Ts. So, 2x50% utilisation could run on the same HT. I don't know how the OSDs are organised into threads, I'm just stating observations from real life (mimic cluster). So, for an SSD OSD I have seen a maximum of 4 threads in R state, two with 100% and two with 50% CPU, a load that fits on 3HT. So, real life says 1HT per HDD and 3HT per SSD plus a bit for kernel and networking and you are set - based on worst-case performance monitoring I have seen in 2 years. Note that this is worst-case load. The average load is much lower. A 16 core machine is totally overpowered. Assuming 1C=2HT, I count (2*3+8*1)/2=7 or (1*3+10*1)/2=6.5. So an 8 core CPU should do in either case. A 10 core CPU might be better, but 16C is a waste of money. I should mention that these estimates apply to Intel CPUs (x86_64 architectures). Other architectures might not provide the same cycle efficiency. Best regards, ================= Frank Schilder AIT Risø Campus Bygning 109, rum S14 ________________________________________ From: Tony Liu <[email protected]> Sent: 13 November 2020 08:32:55 To: Frank Schilder; Nathan Fish Cc: [email protected] Subject: RE: [ceph-users] Re: which of cpu frequency and number of threads servers osd better? You all mentioned first 2T and another 2T. Could you give more details how OSD works with multi-thread, or share the link if it's already documented somewhere? Is it always 4T, or start with 1T and grow up to 4T? Is it max 4T? Does each T run different job or just multiple instances of the same job? Does disk type affect how T works, like 1T is good enough for HDD while 4T is required for SSD? If I change my plan to 2 SSD OSDs and 8 HDD OSDs (with 1 SSD for WAL and DB). If each OSD requires 4T, then 16C/32T 3.0GHz could be a better choice, because it provides sufficient Ts? If SSD OSD requires 4T and HDD OSD only requires 1T, then 8C/16T 3.2GHz would be better, because it provides sufficient Ts as well as stronger computing? Thanks! Tony > -----Original Message----- > From: Frank Schilder <[email protected]> > Sent: Thursday, November 12, 2020 10:59 PM > To: Tony Liu <[email protected]>; Nathan Fish <[email protected]> > Cc: [email protected] > Subject: Re: [ceph-users] Re: which of cpu frequency and number of > threads servers osd better? > > I think this depends on the type of backing disk. We use the following > CPUs: > > Intel(R) Xeon(R) CPU E5-2660 v4 @ 2.00GHz > Intel(R) Xeon(R) Gold 5218 CPU @ 2.30GHz > Intel(R) Xeon(R) Silver 4216 CPU @ 2.10GHz > > My experience is, that a HDD OSD hardly gets to 100% of 1 hyper thread > load even under heavy recovery/rebalance operations on 8+2 and 6+2 EC > pools with compression set to aggressive. The CPU is mostly doing wait- > IO, that is, the disk is the real bottle neck, not the processor power. > With SSDs I have seen 2HT at 100% and 2 more at 50% each. I guess NVMe > might be more demanding. > > A server with 12 HDD and 1 SSD should be fine with a modern CPU with 8 > cores. 16 threads sounds like an 8 core CPU. The 2nd generation Intel® > Xeon® Silver 4209T with 8 cores should easily handle that (single socket > system). We have the 16-core Intel silver in a dual socket system > currently connected to 5HDD and 7SSD and I did a rebalance operation > yesterday. The CPU user load did not exceed 2%, it can handle OSD > processes easily. The server is dimensioned to run up to 12HDD and 14SSD > OSDs (Dell R740xd2). As far as I can tell, the CPU configuration is > overpowered for that. > > Just for info, we use ganglia to record node utilisation. I use 1-year > records and pick peak loads I observed for dimensioning the CPUs. These > records include some very heavy recovery periods. > > Best regards, > ================= > Frank Schilder > AIT Risø Campus > Bygning 109, rum S14 > > ________________________________________ > From: Tony Liu <[email protected]> > Sent: 13 November 2020 04:57:53 > To: Nathan Fish > Cc: [email protected] > Subject: [ceph-users] Re: which of cpu frequency and number of threads > servers osd better? > > Thanks Nathan! > Tony > > -----Original Message----- > > From: Nathan Fish <[email protected]> > > Sent: Thursday, November 12, 2020 7:43 PM > > To: Tony Liu <[email protected]> > > Cc: [email protected] > > Subject: Re: [ceph-users] which of cpu frequency and number of threads > > servers osd better? > > > > From what I've seen, OSD daemons tend to bottleneck on the first 2 > > threads, while getting some use out of another 2. So 32 threads at 3.0 > > would be a lot better. Note that you may get better performance > > splitting off some of that SSD for block.db partitions or at least > > block.wal for the HDDs. > > > > On Thu, Nov 12, 2020 at 9:57 PM Tony Liu <[email protected]> > wrote: > > > > > > Hi, > > > > > > For example, 16 threads with 3.2GHz and 32 threads with 3.0GHz, > > > which makes 11 OSDs (10x12TB HDD and 1x960GB SSD) with better > performance? > > > > > > > > > Thanks! > > > Tony > > > _______________________________________________ > > > ceph-users mailing list -- [email protected] To unsubscribe send an > > > email to [email protected] > _______________________________________________ > ceph-users mailing list -- [email protected] To unsubscribe send an > email to [email protected] _______________________________________________ ceph-users mailing list -- [email protected] To unsubscribe send an email to [email protected]
