Hi,

the default rbd chunk size is 4MB, it's the "order" that defines the chunk size:

rbd info pool/volume1
rbd image 'volume1':
        size 8 GiB in 2048 objects
        order 22 (4 MiB objects)

You can create images with a different order using the '--object-size' parameter:

rbd create temp/rbd-16K --object-size 16K --size 100M

rbd info temp/rbd-16K
rbd image 'rbd-16K':
        size 100 MiB in 6400 objects
        order 14 (16 KiB objects)

There also '--stripe-unit' and '--stripe-count' parameters to keep in mind, but I'd start simple as possible.

Just a few months back we had to migrate a customer galera cluster (OpenStack) into CephFS (on SSD pool) because the response times were awful from the local (rotating) disks of the control nodes. I also thought about attaching a RBD from a SSD pool, but since the nodes were already connected to CephFS, we decided to stay with CephFS.


Zitat von filip Mutterer <fi...@3dds.io>:

Hi!

Is Block alignment for Databases a thing with RBD?

I heard something with 16K alignment ...

If yes how can be checked what alignment a RBD got.

And yes I need to run my Database in Ceph as I have no other storage with redundandency.

Hints for optimizing a single Block device for a Database are very welcome.


Greetings

filip
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