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
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.
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?
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