On 06/08/14 13:07, debian Only wrote:
> Thanks for your reply.
> I have found and test a way myself.. and now share to others
>
>
> >>>>>Begin>>>  On Debian >>>
> root@ceph01-vm:~# modprobe brd rd_nr=1 rd_size=4194304 max_part=0
> root@ceph01-vm:~# mkdir /mnt/ramdisk
> root@ceph01-vm:~# mkfs.btrfs /dev/ram0

You should avoid creating filesystems on top of the ramdisk for the
journal. Either create a single ramdisk, and create partitions on it for
each journal, or create multiple ramdisks and use each ramdisk whole.
Put the journals on these raw partitions / block devs. Using a
filesystem (especially one such as btrfs) on top of a ramdisk just
creates unnecessary overhead.

Alternatively use a tmpfs instead of ramdisk. Just create a single tmpfs
that is big enough to hold all your journals, then symlink each
/var/lib/ceph/osd/ceph-XX/journal to a unique file on the tmpfs.

Beware however that tmpfs _can_ be swapped out to disk, if the system
starts to run low on physical memory.

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