[lustre-devel] RFC: Spill device for Lustre OSD

[Andreas Dilger]

On Nov 4, 2025, at 5:28 PM, Jinshan Xiong <jinshanx at google.com> wrote:
> On Tue, Nov 4, 2025 at 4:20 PM Andreas Dilger wrote:
>> I don't see how the layout xattr format is related to filesystem-level
>> scanning?  This is "just" the xattr format *STORED ON THE OST OBJECT*,
>> and it could be handled by direct device-level (OST) scan tools as well.
> 
> I see. I initially thought you proposed the spill device would function as a mirror and that the existing software stack would handle it.
> 
> Are we going to store the spilled object's status in the layout? It sounds difficult because you will have to initiate a layout change from the OSTs. I think we still need to store such an xattr locally in the OST object.

I'm exactly proposing that the layout xattr be stored on the OST object.
It would have the same format as the existing Lustre layout stored on
the MDT, but *maybe* a different name (e.g. "trusted.spl", "trusted.osd",
or whatever).

I'm not sure if using "trusted.lov" will confuse filesystem scanning
tools or help them...  It probably makes sense to have a different
xattr name, just in case we want MDT spilling (e.g. NVRAM->QLC) in
the future.

>> This would allow mirrors (FLR), multiple spill devices (multiple FLR
>> mirrors), concatenated devices (PFL), etc.  It just avoids adding new
>> formats that need to be parsed, printed, etc.

Cheers, Andreas





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