Hi all,
So i didn't expect these results to be worse because i would assume a drive write cache would make it faster.
I've tested some new Samsung SM863 960GB and Intel DC S4600 240GB SSD's using the method described at Sebastien Han's blog:
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
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
Caspar
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