Hi,
If you don't specifiy WAL it will be located on the same drive as the rocksdb. You
need to specify wal if you have faster disk the your rocksdb, like DATA on HDD, Rocksdb on
SSD, wal on nvme/optane.
In the past they suggested like this:
300GB data 30GB rocksdb, 3GB wal. Not sure is this still true.
Istvan Szabo
Senior Infrastructure Engineer
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Agoda Services Co., Ltd.
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-----Original Message-----
From: Dave Hall <kdhall(a)binghamton.edu>
Sent: Wednesday, March 10, 2021 11:27 PM
To: ceph-users <ceph-users(a)ceph.io>
Subject: [ceph-users] Bluestore OSD Layout - WAL, DB, Journal
Email received from outside the company. If in doubt don't click links nor open
attachments!
________________________________
Hello,
I'm in the process of doubling the number of OSD nodes in my Nautilus cluster - from
3 to 6. Based on answers receive from earlier posts to this list, the new nodes have more
NVMe that the old nodes. More to the point, on the original nodes the amount of NVMe
allocated to each OSD was about 120GB, so the RocksDB was limited to 30GB. However, for
my workload 300GB is probably recommended.
As I prepare to lay out the NVMe on these new nodes, I'm still trying to understand
how to size the DB and WAL for my OSDs and whether Journal is even needed.
According to
https://docs.ceph.com/en/nautilus/ceph-volume/lvm/prepare/
<https://docs.ceph.com/en/nautilus/ceph-volume/lvm/prepare/>
Bluestore supports the following configurations:
* A block device, a block.wal, and a block.db device
* A block device and a block.wal device
* A block device and a block.db device
* A single block device
First question: On my first nodes I managed to get a DB, but no WAL.
My current perception is that WAL and DB occupy separate physical/logical partitions. By
specifying a WAL size and a DB size, ceph-volume will create the corresponding logical
volumes on the NVMe.
Is this correct? It is also possible to lay these out as basic logical partitions?
Second question: How do I decide whether I need WAL, DB, or both?
Third question: Once I answer the above WAL/DB question, what are the guidelines for
sizing them?
Thanks.
-Dave
--
Dave Hall
Binghamton University
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