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performance: 0.856
device: 0.794
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mistranslation: 0.486
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arm: 0.330
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storage physical_block_size is restricted to uint16_t
It is desirable to set -global scsi-hd.physical_block_size=4194304 for RBD-backed storage.
But unfortunatelly, this values is restricted with uint16_t, i.e. 65536 maximum.
For example, scsi-hd.discard_granularity=4194304 is not so restricted (and works as expected)
I think the SCSI spec is limited to 16 bits for representing the block length (in bytes) (see READ CAPACITY(10) command). It's also probably sub-optimal to force a full 4MiB write even for small IOs. You might achieve what you are looking for by setting the minimal and optimal IO size hints to 4MiB (exposed via SCSI block limits VPD page) using "min_io_size" and "opt_io_size" settings.
Yes, you are right. Thanks for the response.
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