Re: Reading from replica

[Gregory Farnum <greg@xxxxxxxxxxx>]

Read-from-replica does not happen unless you go through some contortions with config and developer setups. However, all n OSDs should be the primary for about 1/n% of the data, so you should be seeing reads to to both OSDs as long as you touch several objects at a time.

-Greg

On Wednesday, August 28, 2013, daniel pol wrote:

Hi !
 
I need a little help understanding reads from replicas. I've read a few conflicting messages and the documentation is not very clear to me on this subject (maybe I didn't find the proper doc).
Here's the question: With default replication of 2 (size=2), when doing reads (big sequential reads in my case) are we expecting to see read going to the "primary" object AND  it's replicas ? (similar to RAID1 where you read from both sides of the mirror)
 
I'm not seeing that on my setup right now. I have a pool with 16 PGs on 2 OSDs.  When I do reads only one 1 OSD gets IO.
If that's normal (replica involved in IO only when primary is down) I'll take a note, otherwise I'll have to find why I don't get reads from replicas.
 
Have a nice day,
Dani

-- 
Software Engineer #42 @ http://inktank.com | http://ceph.com
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