Hi Massimo,
On 9/29/2019 9:13 AM, Massimo Sgaravatto wrote:
In my ceph cluster I am use spinning disks for bluestore OSDs and SSDs
just for the block.db.
If I have got it right, right now:
a) only 3,30,300GB can be used on the SSD rocksdb spillover to slow
device, so you don't have any benefit with e.g. 250 GB reserved on the
SSD for block.db wrt a configuration where only 30 GB on the SSD
Generally this is correct except peak points when DB might temporary
need some extra space. For compaction or other interim purposes. I've
observed up to 2x increase in the lab. So allocating some extra space
might be useful.
b) because of a), the recommendation reported in the doc saying that
te block.db size should not be smaller than 4% of block is basically
wrong.
I'd say this is very conservative estimate IMO.
Are there plans to change that in next releases ?
I am asking because I am going to buy new hardware and I'd like to
understand if I should keep considering this 'constraint' when
choosing the size of the SSD disks
Yes, we're working on a more intelligent DB space utilization scheme.
Which will allow interim volume sizes to be useful.
Here is a PR which is pending final (hopefully) review:
https://github.com/ceph/ceph/pull/29687
Thanks, Massimo
Thanks,
Igor
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