Hello guys,
Thank you so much for your responses really appreciate it. But I would like to mention one more thing which I forgot in my last email is that I am going to use this storage for openstack VM's. So still the answer will be the same that I should use 1GB for wal?
On Wed, 14 Aug 2019 at 05:54, Mark Nelson <mnelson@xxxxxxxxxx> wrote:
On 8/13/19 3:51 PM, Paul Emmerich wrote:
> On Tue, Aug 13, 2019 at 10:04 PM Wido den Hollander <wido@xxxxxxxx> wrote:
>> I just checked an RGW-only setup. 6TB drive, 58% full, 11.2GB of DB in
>> use. No slow db in use.
> random rgw-only setup here: 12TB drive, 77% full, 48GB metadata and
> 10GB omap for index and whatever.
>
> That's 0.5% + 0.1%. And that's a setup that's using mostly erasure
> coding and small-ish objects.
>
>
>> I've talked with many people from the community and I don't see an
>> agreement for the 4% rule.
> agreed, 4% isn't a reasonable default.
> I've seen setups with even 10% metadata usage, but these are weird
> edge cases with very small objects on NVMe-only setups (obviously
> without a separate DB device).
>
> Paul
I agree, and I did quite a bit of the early space usage analysis. I
have a feeling that someone was trying to be well-meaning and make a
simple ratio for users to target that was big enough to handle the
majority of use cases. The problem is that reality isn't that simple
and one-size-fits all doesn't really work here.
For RBD you can usually get away with far less than 4%. A small
fraction of that is often sufficient. For tiny (say 4K) RGW objects
(especially objects with very long names!) you potentially can end up
using significantly more than 4%. Unfortunately there's no really good
way for us to normalize this so long as RGW is using OMAP to store
bucket indexes. I think the best we can do long run is make it much
clearer how space is being used on the block/db/wal devices and easier
for users to shrink/grow the amount of "fast" disk they have on an OSD.
Alternately we could put bucket indexes into rados objects instead of
OMAP, but that would be a pretty big project (with it's own challenges
but potentially also with rewards).
Mark
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Thanks and Regards,
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Hemant Sonawane
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