[ceph-users] Bluestore OSD_DATA, WAL & DB

Sage Weil sweil at redhat.com
Mon Sep 25 15:26:41 PDT 2017

On Tue, 26 Sep 2017, Nigel Williams wrote:
> On 26 September 2017 at 08:11, Mark Nelson <mnelson at redhat.com> wrote:
> > The WAL should never grow larger than the size of the buffers you've
> > specified.  It's the DB that can grow and is difficult to estimate both
> > because different workloads will cause different numbers of extents and
> > objects, but also because rocksdb itself causes a certain amount of
> > space-amplification due to a variety of factors.
> Ok, I was confused whether both types could spill. within Bluestore it
> simply blocks if the WAL hits 100%?

It never blocks; it will always just spill over onto the next fastest 
device (wal -> db -> main).  Note that there is no value to a db partition 
if it is on the same device as the main partition.

> Would a drastic (quick) action to correct a too-small-DB-partition
> (impacting performance) is to destroy the OSD and rebuild it with a
> larger DB partition?

That's the easiest!

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