Don't forget if you have server failure you might loose many objects. If the 
failure domain is osd, it means let's say you have 12 drives in each server, 
8+2 EC in an unlucky situation can be located in 1 server also.

Istvan Szabo
Senior Infrastructure Engineer
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Agoda Services Co., Ltd.
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-----Original Message-----
From: Dave Hall <[email protected]>
Sent: Wednesday, March 10, 2021 11:42 PM
To: ceph-users <[email protected]>
Subject: [ceph-users] Failure Domain = NVMe?

Email received from outside the company. If in doubt don't click links nor open 
attachments!
________________________________

Hello,

In some documentation I was reading last night about laying out OSDs, it was 
suggested that if more that one OSD uses the same NVMe drive, the 
failure-domain should probably be set to node. However, for a small cluster the 
inclination is to use EC-pools and failure-domain = OSD.

I was wondering if there is a middle ground - could we define failure-domain = 
NVMe?  I think the map would need to be defined manually in the same way that 
failure-domain = rack requires information about which nodes are in each rack.

Example:  My latest OSD nodes have 8 HDDs and 3 U.2 NVMe.  I'd set up the 
WAL/DB for with HDDs per OSD  (wasted space on the 3rd NVMe).
Across all my OSD nodes I will have 8 HDDs and either 2 or 3 NVMe
devices per node - 15 total NVMe devices.   My preferred EC-pool profile
is 8+2.  It seems that this profile could be safely dispersed across 15 failure 
domains, resulting in protection against NVMe failure.

Please let me know if this is worth pursuing.

Thanks.

-Dave

--
Dave Hall
Binghamton University
[email protected]
607-760-2328 (Cell)
607-777-4641 (Office)
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