[Qemu-devel] [Bug 1811720] Re: storage physical_block_size is restricted to uint16_t

[Jason Dillaman]

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.

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https://bugs.launchpad.net/bugs/1811720

Title:
  storage physical_block_size is restricted to uint16_t

Status in QEMU:
  New

Bug description:
  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)

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