Il giorno mer 3 feb 2021 alle ore 21:22 Dan van der Ster <dan@vanderster.com> ha scritto:
Lastly, if you can't afford 3x replicas, then use 2+2 erasure coding if possible.
I will investigate I heard that erasure coding is slow. Anyway I will write here the reason of this thread: In my customers I have usually proxmox+ceph with: - three servers - three monitors - 6 osd (two per server) - size=3 and min_size=2 I followed the recommendations to stay safe. But one day one disk of one server has broken, osd where at 55%. What happened then? Ceph started filling the remaining OSD to maintain size=3 OSD reached 90% ceph stopped all. Customer VMs froze and customer lost time and some data that was not written on disk. So I got angry.... size=3 and customer still loses time and data?
Cheers, Dan
On Wed, Feb 3, 2021, 8:49 PM Mario Giammarco <mgiammarco@gmail.com> wrote:
Thanks Simon and thanks to other people that have replied. Sorry but I try to explain myself better. It is evident to me that if I have two copies of data, one brokes and while ceph creates again a new copy of the data also the disk with the second copy brokes you lose the data. It is obvious and a bit paranoid because many servers on many customers run on raid1 and so you are saying: yeah you have two copies of the data but you can broke both. Consider that in ceph recovery is automatic, with raid1 some one must manually go to the customer and change disks. So ceph is already an improvement in this case even with size=2. With size 3 and min 2 it is a bigger improvement I know.
What I ask is this: what happens with min_size=1 and split brain, network down or similar things: do ceph block writes because it has no quorum on monitors? Are there some failure scenarios that I have not considered? Thanks again! Mario
Il giorno mer 3 feb 2021 alle ore 17:42 Simon Ironside < sironside@caffetine.org> ha scritto:
On 03/02/2021 09:24, Mario Giammarco wrote:
Hello, Imagine this situation: - 3 servers with ceph - a pool with size 2 min 1
I know perfectly the size 3 and min 2 is better. I would like to know what is the worst thing that can happen:
Hi Mario,
This thread is worth a read, it's an oldie but a goodie:
http://lists.ceph.com/pipermail/ceph-users-ceph.com/2016-December/014846.htm...
Especially this post, which helped me understand the importance of min_size=2
http://lists.ceph.com/pipermail/ceph-users-ceph.com/2016-December/014892.htm...
Cheers, Simon _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io
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