On 1/10/2014 10:46 PM, Martin K. Petersen wrote:
"Andy" == Andy Grover <agrover@xxxxxxxxxx> writes:
Andy> Yes, don't you need FORMAT UNIT because protection information is
Andy> going to mean the pi-enabled lun will need to report less blocks?
Modern disk drives won't shrink when you reformat them with PI. This is
a result of an IDEMA agreement about LBA counts.
And if you create a 10GB PI LUN on an array you'll get 10GB for data.
Andy> The ramdisk backstore changes in this series allocate extra space
Andy> for PI info, but my understanding was that especially for
Andy> emulation with block and fileio backstores, everything needs to go
Andy> in the same amount of space.
For both file and block I'd recommend we store the PI in a separate
block device or file unless the backing device is PI-capable.
Andy> Furthermore, if we want PI info stored along with the blocks, then
Andy> block and fileio backstore formats are no longer going to be 1:1
Andy> -- requiring offset calculations, non-aligned read-modify-write,
Andy> and all that unpleasantness to be handled?
I only think interleaved makes sense if you're passing the PI through
instead of emulating.
I agree, I implemented interleaved mode just as a proof of concept that
our HW can perform offload in that manner.
I assume we can stick with non-interleaved, although it can be added as
a user option.
Sagi.
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