I asked the same question a couple of weeks ago. No response I got
contradicted the documentation but nobody actively confirmed the
documentation was correct on this subject, either; my end state was that
I was relatively confident I wasn't making some horrible mistake by
simply specifying a big DB partition and letting bluestore work itself
out (in my case, I've just got HDDs and SSDs that were journals under
filestore), but I could not be sure there wasn't some sort of
performance tuning I was missing out on by not specifying them separately.
Rich
On 21/09/17 20:37, Benjeman Meekhof wrote:
Some of this thread seems to contradict the documentation and confuses
me. Is the statement below correct?
"The BlueStore journal will always be placed on the fastest device
available, so using a DB device will provide the same benefit that the
WAL device would while also allowing additional metadata to be stored
there (if it will fix)."
http://docs.ceph.com/docs/master/rados/configuration/bluestore-config-ref/#devices
it seems to be saying that there's no reason to create separate WAL
and DB partitions if they are on the same device. Specifying one
large DB partition per OSD will cover both uses.
thanks,
Ben
On Thu, Sep 21, 2017 at 12:15 PM, Dietmar Rieder
<dietmar.rie...@i-med.ac.at> wrote:
On 09/21/2017 05:03 PM, Mark Nelson wrote:
On 09/21/2017 03:17 AM, Dietmar Rieder wrote:
On 09/21/2017 09:45 AM, Maged Mokhtar wrote:
On 2017-09-21 07:56, Lazuardi Nasution wrote:
Hi,
I'm still looking for the answer of these questions. Maybe someone can
share their thought on these. Any comment will be helpful too.
Best regards,
On Sat, Sep 16, 2017 at 1:39 AM, Lazuardi Nasution
<mrxlazuar...@gmail.com <mailto:mrxlazuar...@gmail.com>> wrote:
Hi,
1. Is it possible configure use osd_data not as small partition on
OSD but a folder (ex. on root disk)? If yes, how to do that with
ceph-disk and any pros/cons of doing that?
2. Is WAL & DB size calculated based on OSD size or expected
throughput like on journal device of filestore? If no, what is the
default value and pro/cons of adjusting that?
3. Is partition alignment matter on Bluestore, including WAL & DB
if using separate device for them?
Best regards,
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I am also looking for recommendations on wal/db partition sizes. Some
hints:
ceph-disk defaults used in case it does not find
bluestore_block_wal_size or bluestore_block_db_size in config file:
wal = 512MB
db = if bluestore_block_size (data size) is in config file it uses 1/100
of it else it uses 1G.
There is also a presentation by Sage back in March, see page 16:
https://www.slideshare.net/sageweil1/bluestore-a-new-storage-backend-for-ceph-one-year-in
wal: 512 MB
db: "a few" GB
the wal size is probably not debatable, it will be like a journal for
small block sizes which are constrained by iops hence 512 MB is more
than enough. Probably we will see more on the db size in the future.
This is what I understood so far.
I wonder if it makes sense to set the db size as big as possible and
divide entire db device is by the number of OSDs it will serve.
E.g. 10 OSDs / 1 NVME (800GB)
(800GB - 10x1GB wal ) / 10 = ~79Gb db size per OSD
Is this smart/stupid?
Personally I'd use 512MB-2GB for the WAL (larger buffers reduce write
amp but mean larger memtables and potentially higher overhead scanning
through memtables). 4x256MB buffers works pretty well, but it means
memory overhead too. Beyond that, I'd devote the entire rest of the
device to DB partitions.
thanks for your suggestion Mark!
So, just to make sure I understood this right:
You'd use a separeate 512MB-2GB WAL partition for each OSD and the
entire rest for DB partitions.
In the example case with 10xHDD OSD and 1 NVME it would then be 10 WAL
partitions with each 512MB-2GB and 10 equal sized DB partitions
consuming the rest of the NVME.
Thanks
Dietmar
--
_________________________________________
D i e t m a r R i e d e r, Mag.Dr.
Innsbruck Medical University
Biocenter - Division for Bioinformatics
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