I think it's time to start pointing out the the 3/30/300 logic not really
holds any longer true post Octopus:
On Thu, 2 Jul 2020 at 00:09, Burkhard Linke <
On 7/1/20 1:57 PM, Andrei Mikhailovsky wrote:
We are planning to perform a small upgrade to our cluster and slowly
12TB SATA HDD drives. We need to accommodate for additional
SSD WAL/DB requirements as well. Currently we are considering the following:
HDD Drives - Seagate EXOS 12TB
SSD Drives for WAL/DB - Intel D3 S4510 960GB or Intel D3 S4610 960GB
Our cluster isn't hosting any IO intensive DBs nor IO hungry VMs such as
Exchange, MSSQL, etc.
From the documentation that I've read the recommended size for DB is
1% and 4% of the size of the osd. Would 2% figure be sufficient
enough (so around 240GB DB size for each 12TB osd?)
The documentation is wrong. Rocksdb uses different levels to store data,
and need to store each level either completely in the DB partition or on
the data partition. There have been a number of mail threads about the
In your case the best size would be 30GB for the DB part + the WAL size
(usually 2 GB). For compaction and other actions the ideal DB size needs
to be doubled, so you end up with 62GB per OSD. Larger DB partitions are
a waste of capacity, unless it can hold the next level (300GB per OSD).
If you have spare capacity on the SSD (>100GB) you can either leave it
untouched or create a small SSD based OSD for small pools that require a
lower latency, e.g. a small extra fast pool for RBD or the RGW
Also, from your experience, which is a better model for the SSD DB/WAL?
Intel S4510 be sufficient enough for our purpose or would the S4610
be a much better choice? Are there any other cost effective performance to
consider instead of the above models?
The SSD model should support fast sync writes, similar to the known
requirements for filestore journal SSDs. If your selected model is a
good fit according to the test methods, then it is probably also a good
choice for bluestore DBs.
Since not all data is written to the bluestore DB (no full data journal
in contrast to filestore), the amount of data written to the SSD is
probably lower. The DWPD requirements might be lower. To be on the safe
side, use the better model (higher DWPD / "write intensive") if possible.
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