[ceph-users] Re: Bluestore cache parameter precedence

5 Feb 2020

      Hi Boris,

not sure I understand why do you think it needs correction.

IMO _use_rotational_settings() function does what you're suggesting plus 
it has some additional logic to be able to enforce specific device type.

The latter is intended primarily for testing/debugging and enabled via 
'bluestore_debug_enforce_settings' configuration setting.

Thanks,

Igot

On 2/4/2020 8:29 PM, Boris Epstein wrote:
...
Hi Igor,
Thanks!
I think the code needs to be corrected - the choice criteria for which 
setting to use when
cct->_conf->bluestore_cache_size == 0
should be as follows:
1) See what kind of storage you have.
2) Select type-appropriate storage.
Is this code public-editable? I'll be happy to correct that.
Regards,
Boris.
On Tue, Feb 4, 2020 at 12:10 PM Igor Fedotov <ifedotov@suse.de 
<mailto:ifedotov@suse.de>> wrote:
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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