Re: rbd pool:replica size choose: 2 vs 3

[Götz Reinicke - IT Koordinator <goetz.reinicke@xxxxxxxxxxxxxxx>]

Hi,

Am 23.09.16 um 05:55 schrieb Zhongyan Gu:

Hi there,

the default rbd pool replica size is 3. However, I found that in our all ssd environment, capacity become a cost issue. We want to save more capacity. So one option is change the replica size from 3 to 2. anyone can share the experience of pros vs cons regarding replica size 2 vs 3?

from my (still limited) POV, one main aspect is: how reliabel is your hardware if you think off this? How often will a disk break, a server crash, a datacenter burn down, a networkswitch fail? And if there is a failure, how fast could that broken part be replaced or how fast is your availabel hardware to replicate the lost OSD to the remaining system.

I dont have numbers, but for our first initial cluster we go as well with a repl size of 2 and I dont have bad feelings yet when i look at the server and network infrastrukture we got.

Others with more experiacne will give some other hints and may be numbers. I never found some sort of calculator which can say "Oh you get this hardware? Than a repl size of x y z is what you need."
 
HTH a bit . Regards . Götz

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