ceph block size

asked 2019-02-06 03:24:25 -0600

lelunicu gravatar image

hi, when an application within a VM write to ceph cluster then every block written is broken by ceph (OSD) in smaller parts and is written -stripe accross the ceph nodes. right? by doing this the read and write will be faster than using normal block. right? tnx

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It's not really faster because you have the replication, network latency, and some more limitations. But as @Bernd already states, the design is built for reliability so your data is still available even if some of your hard disks fail.

eblock gravatar imageeblock ( 2019-02-06 09:56:32 -0600 )edit

I forgot to mention that you don't have a SOP since every client talks to his "own" OSD daemons directly, so it may not be faster, but the cluster handles way more requests in parallel.

eblock gravatar imageeblock ( 2019-02-07 03:35:40 -0600 )edit

Yes, whereas a single application won’t get performance benefits out of Ceph, the total performance of a Ceph cluster goes up as it scales up. In other words, as it scales it can handle more load.

Bernd Bausch gravatar imageBernd Bausch ( 2019-02-08 23:24:46 -0600 )edit

every i/o is broken down in blocks and each block is written in a ceph node.this block will be then copied to the rest of the ceph node?

lelunicu gravatar imagelelunicu ( 2019-03-08 08:53:34 -0600 )edit

I don't know whether it is done at the block level, but a client writes data to an OSD, which then replicates it to the other OSDs that contain copies of that data. See http://docs.ceph.com/docs/giant/archi..., point 4 "replication".

Bernd Bausch gravatar imageBernd Bausch ( 2019-03-09 22:03:05 -0600 )edit

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answered 2019-02-06 03:43:37 -0600

updated 2019-02-06 03:45:55 -0600

In principle yes, but as far as I know, Ceph's default block size is 4MB, whereas disk accesses are usually around 4Kb or so.

The aim of Ceph is not speed, but reliability and scalability.

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Asked: 2019-02-06 03:24:25 -0600

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Last updated: Feb 06 '19