Re: [GIT PULL 18/25] lightnvm: set target over-provision on create ioctl

From: Matias BjÃrling
Date: Fri Jan 05 2018 - 14:54:01 EST


On 01/05/2018 08:52 PM, Javier Gonzalez wrote:
On 5 Jan 2018, at 20.33, Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:

On 01/05/2018 05:16 AM, Matias BjÃrling wrote:
From: Javier GonzÃlez <javier@xxxxxxxxxxxx>

Allow to set the over-provision percentage on target creation. In case
that the value is not provided, fall back to the default value set by
the target.

In pblk, set the default OP to 11% of the total size of the device

+#define PBLK_DEFAULT_OP (11)

Hi,
Just curious -- where does 11 come from? Is it a spec value?

11 stands for 11% over-provisioning for the media to allow garbage
collection. Different SSDs have different values based on the targeted
workload - 11% is a common default value for standard drives.

The spec. does not specify any default values of over-provisioning.

Javier.


I think what Randy means is, why is the value not 20% or 7%, which is the traditional over-provisioning on SSDs.