Re: Ceph Luminous RocksDB vs WalDB?

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I'm also not 100% sure but I think that the first one is the right way to go. The second command only specifies the db partition but no dedicated WAL partition. The first one should do the trick.


On 28.06.2018 22:58, Igor Fedotov wrote:

I think the second variant is what you need. But I'm not the guru in ceph-deploy so there might be some nuances there...

Anyway the general idea is to have just a single NVME partition (for both WAL and DB) per OSD.

Thanks,

Igor


On 6/27/2018 11:28 PM, Pardhiv Karri wrote:
Thank you Igor for the response.

So do I need to use this,

ceph-deploy osd create --debug --bluestore --data /dev/sdb --block-wal /dev/nvme0n1p1 --block-db /dev/nvme0n1p2 cephdatahost1

or 

ceph-deploy osd create --debug --bluestore --data /dev/sdb --block-db /dev/nvme0n1p2 cephdatahost1

where /dev/sdb is ssd disk for osd
/dev/nvmen0n1p1 is 10G partition
/dev/nvme0n1p2 is 25G partition


Thanks,
Pardhiv K

On Wed, Jun 27, 2018 at 9:08 AM Igor Fedotov <ifedotov@xxxxxxx> wrote:

Hi Pardhiv,

there is no WalDB in Ceph.

It's WAL (Write Ahead Log) that is a way to ensure write safety in RocksDB. In other words - that's just a RocksDB subsystem which can use separate volume though.

In general For BlueStore/BlueFS one can either allocate separate volumes for WAL and DB or have them on the same volume. The latter is the common option.

The separated layout makes sense when you have tiny but super-fast device (for WAL) and less effective (but still fast) larger drive for DB. Not to mention the third one for user data....

E.g. HDD (user data) + SDD (DB) + NVME  (WAL) is such a layout.


So for you case IMO it's optimal to have merged WAL+DB at NVME and data at SSD. Hence no need for separate WAL volume.


Regards,

Igor


On 6/26/2018 10:22 PM, Pardhiv Karri wrote:
Hi,

I am playing with Ceph Luminous and getting confused information around usage of WalDB vs RocksDB.

I have 2TB NVMe drive which I want to use for Wal/Rocks DB and have 5 2TB SSD's for OSD. 
I am planning to create 5 30GB partitions for RocksDB on NVMe drive, do I need to create partitions of WalDB also on NVMe drive or does RocksDB does same work as WalDB plus having metadata on it? 

So my question is do I really need to use WalDB along with RocksDB or having RocksDB only is fine?

Thanks,
Pardhiv K





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Pardhiv Karri
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