On Tue, Jan 02, 2018 at 04:54:55PM +0000, John Spray wrote:
On Tue, Jan 2, 2018 at 10:43 AM, Jan Fajerski <jfajerski@xxxxxxxx> wrote:
Hi lists,
Currently the ceph status output formats all numbers with binary unit
prefixes, i.e. 1MB equals 1048576 bytes and an object count of 1M equals
1048576 objects. I received a bug report from a user that printing object
counts with a base 2 multiplier is confusing (I agree) so I opened a bug and
https://github.com/ceph/ceph/pull/19117.
In the PR discussion a couple of questions arose that I'd like to get some
opinions on:
- Should we print binary unit prefixes (MiB, GiB, ...) since that would be
technically correct?
I'm not a fan of the technically correct base 2 units -- they're still
relatively rarely used, and I've spent most of my life using kB to
mean 1024, not 1000.
We could start changing the "rarely used" part ;) But I can certainly live with
keeping the old units.
- Should counters (like object counts) be formatted with a base 10
multiplier or a multiplier woth base 2?
I prefer base 2 for any dimensionless quantities (or rates thereof) in
computing. Metres and kilograms go in base 10, bytes go in base 2.
It's all very subjective and a matter of opinion of course, and my
feelings aren't particularly strong :-)
As far as I understand the standards regarding this (IEC 60027, ISO/IEC 80000,
probably more) are talking about base 2 units for digital data related units
only. I might of course misunderstand.
What is problematic I find is that other tools will (mostly?) use base 10 units
for everything not data related. Say I plot the object count of ceph in Grafana.
It'll use base 10 multipliers for a dimensionless number. Since Grafana (and I
imagine other toolsllike this) consume raw numbers we'll end up with Grafana
displaying a different object count then "ceph -s". Say 1.04M vs 1M. Now this is
not terrible but it'll get worse with higher counts quickly.
In the original tracker issue it's noted that this was reported with cluster
containing 7150896726 objects. The difference from grafana to "ceph -s" was
7150M vs 6835M.
John
My proposal would be to both use binary unit prefixes and use base 10
multipliers for counters. I think this aligns with user expectations as well
as the relevant standard(s?).
Best,
Jan
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Jan Fajerski
Engineer Enterprise Storage
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton,
HRB 21284 (AG Nürnberg)
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