Well said! Brett On Tue, Apr 23, 2024 at 7:05 AM Janne Johansson <icepic.dz@gmail.com> wrote:
Den tis 23 apr. 2024 kl 11:32 skrev Frédéric Nass <frederic.nass@univ-lorraine.fr>:
Ceph is strongly consistent. Either you read/write objects/blocs/files with an insured strong consistency OR you don't. Worst thing you can expect from Ceph, as long as it's been properly designed, configured and operated is a temporary loss of access to the data.
This is often more important than you think. All centralized storage systems will have to face some kind of latency when sending data over the network, when splitting the data into replicas or erasure coding shards, when waiting for all copies/shards are actually finished written (perhaps via journals) to the final destination and then lastly for the write to be acknowledged back to the writing client. If some vendor says that "because of our special code, this part takes zero time", they are basically telling you that they are lying about the status of the write in order to finish more quickly, because this wins them contracts or wins competitions.
It will not win you any smiles when there is an incident and data that was ACKed to be on disk suddenly isn't because some write cache lost power at the same time as the storage box and now some database have half-written transactions in it. Ceph is by no means the fastest possible way to store data on a network, but it is very good while still retaining the strong consistencies mentioned by Frederic above allowing for many clients to do many IOs in parallel against the cluster.
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