存储池、归置组和 CRUSH 配置参考

当你创建存储池并给它设置归置组数量时，如果你没指定 Ceph 就用默认值。我们建议更改某些默认值，特别是存储池的副本数和默认归置组数量，可以在运行 pool 命令的时候设置这些值。你也可以把配置写入 Ceph 配置文件的 [global] 段来覆盖默认值。

[global]
 
    # By default, Ceph makes 3 replicas of objects. If you want to make four 
    # copies of an object the default value--a primary copy and three replica 
    # copies--reset the default values as shown in 'osd pool default size'.
    # If you want to allow Ceph to write a lesser number of copies in a degraded 
    # state, set 'osd pool default min size' to a number less than the
    # 'osd pool default size' value.
 
    osd pool default size = 4  # Write an object 4 times.
    osd pool default min size = 1 # Allow writing one copy in a degraded state.
 
    # Ensure you have a realistic number of placement groups. We recommend
    # approximately 100 per OSD. E.g., total number of OSDs multiplied by 100 
    # divided by the number of replicas (i.e., osd pool default size). So for
    # 10 OSDs and osd pool default size = 4, we'd recommend approximately
    # (100 * 10) / 4 = 250.
 
    osd pool default pg num = 250
    osd pool default pgp num = 250