Re: ssd only storage and ceph

[Jan Schermer <jan@xxxxxxxxxxx>]

On 17 Mar 2016, at 17:28, Erik Schwalbe <erik.schwalbe@xxxxxxxxx> wrote:

Hi,

at the moment I do some tests with SSD's and ceph.

My Question is, how to mount an SSD OSD? With or without discard option?

I recommend running without discard but running "fstrim" command every now and then (depends on how fast your SSD is - some SSDs hang for quite a while when fstrim is run on them, test it)

Where should I do the fstrim, when I mount the OSD without discard? On the ceph storage node? Inside the vm, running on rbd?

discard on the SSD itself makes garbage collection easier - that might make the SSD faster and it can last longer (how faster and how longer depends on the SSD, generally if you use DC-class SSDs you won't notice anything)

discard in the VM (assuming everything supports it) makes thin-provisioning more effective, but you (IMO) need virtio-scsi for that. I have no real-life experience whether Ceph actually frees the unneeded space even if you make it work...

What is the best practice there.

Thanks for your answers.

Regards,

Erik

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