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 [email protected] http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
