So why do not journal write only metadata?
As I've read, it is for ensure consistency of data, but I do not know how to do that in detail? And why BlueStore still ensure consistency without journal?
2017-09-20 16:03 GMT+07:00 <ceph@xxxxxxxxxxxxxx>:
On 20/09/2017 10:59, Sam Huracan wrote:
> Hi Cephers,
>
> I've read about new BlueStore and have 2 questions:
>
> 1. The purpose of BlueStore is eliminating the drawbacks of POSIX when
> using FileStore. These drawbacks also cause journal, result in double write
> penalty. Could you explain me more detail about POSIX fails when using in
> FileStore? and how Bluestore still guarantee consistency without journal?
From what I guess, bluestore uses the definitive storage location as a
journal
So, filestore:
- write data to the journal
- write metadata
- move data from journal to definitive storage
Bluestore:
- write data to definitive storage (free space, not overwriting anything)
- write metadata
>
> I find a topic on reddit that told by journal, ceph avoid buffer cache, is
> it true? is is drawback of POSIX?
> https://www.reddit.com/r/ceph/comments/5wbp4d/so_will_
> bluestore_make_ssd_journals_pointless/ > ______________________________
>
> 2. We have to put journal on SSD to avoid double write, but it lead to
> losing some OSDs when SSD fails. With BlueStore model, we can put all WAL,
> metadata, data on 1 disk, make it easily for monitoring, maintaining. But
> according to this post of Sebastian Han:
> https://www.sebastien-han.fr/blog/2016/05/04/Ceph-Jewel-
> configure-BlueStore-with-multiple-devices/
> We could put WAL, metadata, and data on separate disks for increasing
> performance, I think it is not different to FileStore model.
> What is OSD deployment is most optimized? Put all on 1 disk or split on
> multi disks?
>
> Thanks in advance
>
>
>
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