here I am not mixing raid1 with ceph. I am doing a comparison: is it safer
to have a server with raid1 disks or two servers with ceph and size=2
We are talking about real world examples where a customer is buying a new
server and want to choose.
Il giorno gio 4 feb 2021 alle ore 05:52 Federico Lucifredi <
federico(a)redhat.com> ha scritto:
It is obvious and a bit paranoid because many
servers on many customers
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
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
it is a bigger improvement I know.
Generally speaking, users running Ceph at any scale do not use RAID to
mirror their drives. They rely on data resiliency as delivered by Ceph
(three replicas on HDD, two replicas on solid state media).
It is expensive to run RAID underneath Ceph, and in some cases even
counter-productive. We do use RAID controllers whenever we can because they
are battery-backed and insure writes hit the local disk even on a power
failure, but that is (ideally) the only case where you hear the words RAID
and Ceph together.
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