Hello, Caspar! Would you mind to share controller model you use? I would say these results are pretty low.
Here are my results on Intel RMS25LB LSI2308 based SAS controller in IT mode: I set write_cache to write through Test command, fio 2.2.10: sudo fio --filename=/dev/sdb --direct=1 --sync=1 --rw=write --bs=4k --numjobs=XXX --iodepth=1 --runtime=60 --time_based --group_reporting --name=journal-test where XXX - number of jobs Results: numjobs: 1 write: io=5068.6MB, bw=86493KB/s, iops=21623, runt= 60001msec clat (usec): min=38, max=8343, avg=45.01, stdev=32.10 numjobs : 5 write: io=14548MB, bw=248274KB/s, iops=62068, runt= 60001msec clat (usec): min=40, max=11291, avg=79.05, stdev=46.37 numjobs : 10 write: io=14762MB, bw=251939KB/s, iops=62984, runt= 60001msec clat (usec): min=52, max=10356, avg=157.16, stdev=65.69 I have got even better results on z97 integrated SATA controller, you can find them in comments to the post you have mentioned ( https://www.sebastien-han.fr/blog/2014/10/10/ceph-how-to- test-if-your-ssd-is-suitable-as-a-journal-device/#comment-3273882789). Still don't know why LSI 2308 SAS performance worse than z97 SATA and can't find any info on why write back cache setting has slower write than write through. But I would offer to pay more attention to IOPS than to the sequential write speed, especially on the small blocks workload. 2018-03-13 21:33 GMT+05:00 Caspar Smit <caspars...@supernas.eu>: > Hi all, > > I've tested some new Samsung SM863 960GB and Intel DC S4600 240GB SSD's > using the method described at Sebastien Han's blog: > > https://www.sebastien-han.fr/blog/2014/10/10/ceph-how-to- > test-if-your-ssd-is-suitable-as-a-journal-device/ > > The first thing stated there is to disable the drive's write cache, which > i did. > > For the Samsungs i got these results: > > 1 Job: 85 MB/s > 5 Jobs: 179 MB/s > 10 Jobs: 179 MB/s > > I was curious what the results would be with the drive write cache on, so > i turned it on. > > Now i got these results: > > 1 Job: 49 MB/s > 5 Jobs: 110 MB/s > 10 Jobs: 132 MB/s > > So i didn't expect these results to be worse because i would assume a > drive write cache would make it faster. > > For the Intels i got more or less the same conclusion (with different > figures) but the performance with drive write cache was about half the > performance as without drive write cache. > > Questions: > > 1) Is this expected behaviour (for all/most SSD's)? If yes, why? > 2) Is this only with this type of test? > 3) Should i always disable drive write cache for SSD's during boot? > 4) Is there any negative side-effect of disabling the drive's write cache? > 5) Are these tests still relevant for DB/WAL devices? The blog is written > for Filestore and states all journal writes are sequential but is that also > true for bluestore DB/WAL writes? Do i need to test differently for DB/WAL? > > Kind regards, > Caspar > > _______________________________________________ > ceph-users mailing list > firstname.lastname@example.org > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > -- С уважением, Дробышевский Владимир Компания "АйТи Город" +7 343 2222192 ИТ-консалтинг Поставка проектов "под ключ" Аутсорсинг ИТ-услуг Аутсорсинг ИТ-инфраструктуры
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