I think it's time to start pointing out the the 3/30/300 logic not really holds any longer true post Octopus: https://lists.ceph.io/hyperkitty/list/ceph-users@xxxxxxx/message/CKRCB3HUR7UDRLHQGC7XXZPWCWNJSBNT/ On Thu, 2 Jul 2020 at 00:09, Burkhard Linke < Burkhard.Linke@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > Hi, > > On 7/1/20 1:57 PM, Andrei Mikhailovsky wrote: > > Hello, > > > > We are planning to perform a small upgrade to our cluster and slowly > start adding 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 > between 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 > correct sizing. > > > 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 > configuration pools. > > > > > Also, from your experience, which is a better model for the SSD DB/WAL? > Would 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. > > Regards, > > Burkhard > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx > _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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