Re: 2x replication: A BIG warning

David Turner <david.turner@xxxxxxxxxxxxxxxx> · Fri, 9 Dec 2016 22:13:23 +0000

I'm pretty certain that the write returns as complete only after all active OSDs for a PG have completed the write regardless of min_size.

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From: ceph-users [ceph-users-bounces@xxxxxxxxxxxxxx] on behalf of Oliver Humpage [oliver@xxxxxxxxxxxxxxx]

Sent: Friday, December 09, 2016 2:31 PM

To: ceph-users@xxxxxxxx

Subject: Re: [ceph-users] 2x replication: A BIG warning

On 7 Dec 2016, at 15:01, Wido den Hollander <wido@xxxxxxxx> wrote:

I
 would always run with min_size = 2 and manually switch to min_size = 1 if the situation really requires it at that moment.

Thanks for this thread, it’s been really useful.

I might have misunderstood, but does min_size=2 also mean that writes have to wait for at least 2 OSDs to have data written before the write is confirmed? I always assumed this would have a noticeable effect on performance and so left it at 1.

Our use case is RBDs being exported as iSCSI for ESXi. OSDs are journalled on enterprise SSDs, servers are linked with 10Gb, and we’re generally getting very acceptable speeds. Any idea as to how upping min_size to 2 might affect things, or should we just
 try it and see?

Oliver.

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