Hi,
>> Assuming production level, we would keep a pretty close 1:2 SSD:HDD ratio,
>1:4-5 is common but depends on your needs and the devices in question, ie. assuming LFF drives and that you aren’t using crummy journals.
You might be speaking about different ratios here. I think that Anthony is speaking about journal/OSD and Reed speaking about capacity ratio between and HDD and SSD tier/root.
I have been experimenting with hybrid setups (1 copy on SSD + 2 copies on HDD), like Richard says you’ll get much better random read performance with primary OSD on SSD but write performance won’t be amazing since you still have 2 HDD copies to write before ACK.
I know the doc suggests using primary affinity but since it’s a OSD level setting it does not play well with other storage tiers so I searched for other options. From what I have tested, a rule that selects the first/primary OSD from the ssd-root then the rest of the copies from the hdd-root works. Though I am not sure it is *guaranteed* that the first OSD selected will be primary.
“rule hybrid {
ruleset 2
type replicated
min_size 1
max_size 10
step take ssd-root
step chooseleaf firstn 1 type host
step emit
step take hdd-root
step chooseleaf firstn -1 type host
step emit
}”
Cheers,
Maxime
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