Ok, that’s good to know. I was planning on using an EC pool. Maybe I'll store some of the larger kv pairs in their own objects or move the metadata into it's own replicated pool entirely. If the storage mechanism is the same, is there a reason xattrs are supported and omap is not? (Or is there some hidden cost to storing kv pairs in an EC pool I’m unaware of, e.g., does the kv data get replicated across all OSDs being used for a PG or something?)
Thanks,
Ben
On Tue, Sep 11, 2018 at 1:46 PM Patrick Donnelly <pdonnell@xxxxxxxxxx> wrote:
On Tue, Sep 11, 2018 at 12:43 PM, Benjamin Cherian
<benjamin.cherian@xxxxxxxxx> wrote:
> On Tue, Sep 11, 2018 at 10:44 AM Gregory Farnum <gfarnum@xxxxxxxxxx> wrote:
>>
>> <snip>
>> In general, if the key-value storage is of unpredictable or non-trivial
>> size, you should use omap.
>>
>> At the bottom layer where the data is actually stored, they're likely to
>> be in the same places (if using BlueStore, they are the same — in FileStore,
>> a rados xattr *might* be in the local FS xattrs, or it might not). It is
>> somewhat more likely that something stored in an xattr will get pulled into
>> memory at the same time as the object's internal metadata, but that only
>> happens if it's quite small (think the xfs or ext4 xattr rules).
>
>
> Based on this description, if I'm planning on using Bluestore, there is no
> particular reason to ever prefer using xattrs over omap (outside of ease of
> use in the API), correct?
You may prefer xattrs on bluestore if the metadata is small and you
may need to store the xattrs on an EC pool. omap is not supported on
ecpools.
--
Patrick Donnelly
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