Re: Bluestore cache parameter precedence

[Igor Fedotov <ifedotov@xxxxxxx>]

Hi Boris,

general settings (unless they are set to zero) override disk-specific 
settings .

I.e. bluestore_cache_size overrides both bluestore_cache_size_hdd and 
bluestore_cache_size_ssd.

Here is the code snippet in case you know C++

  if (cct->_conf->bluestore_cache_size) {
    cache_size = cct->_conf->bluestore_cache_size;
  } else {
    // choose global cache size based on backend type
    if (_use_rotational_settings()) {
      cache_size = cct->_conf->bluestore_cache_size_hdd;
    } else {
      cache_size = cct->_conf->bluestore_cache_size_ssd;
    }
  }

Thanks,

Igor

On 2/4/2020 2:14 PM, Boris Epstein wrote:
> Hello list,
>
> As stated in this document:
>
> https://docs.ceph.com/docs/master/rados/configuration/bluestore-config-ref/
>
> there are multiple parameters defining cache limits for BlueStore. You have
> bluestore_cache_size (presumably controlling the cache size),
> bluestore_cache_size_hdd (presumably doing the same for HDD storage only)
> and bluestore_cache_size_ssd (presumably being the equivalent for SSD). My
> question is, does bluestore_cache_size override the disk-specific
> parameters, or do I need to set the disk-specific (or, rather, storage type
> specific ones separately if I want to keep them to a certain value.
>
> Thanks in advance.
>
> Boris.
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