Re: Using fio for testing for SMR

["Ian S. Worthington" <ianworthington@usa.net>]

Hi Damien --


> > This tells us that the maximum size the device can support is 256KB
> > (max_hw_sectors_kb)
> > and the maximum size that the kernel allows is 256KB (max_sectors_kb). 
> 
> Which highly depends on the HBA since the hard-disk interface will accept
much
> larger commands. This 256KB on your system seems to be very low. What HBA
are
> you using ? These days, most SAS HBAs have at least 128 or 256 segments,
which
> allow up to 512KB/1MB IOs. SATA/AHCI is limited at 169 segments for up to
32MB
> max_hw_sectors_kb (and 1280 KB max_sectors_kb).
> 
> > Additionally, the DMA engine is limited to 2048 segments of IO, 
> > each with a max size of 64KB.
> 
> That's a lot. I wonder why max_hw_sectors_kb end up so small.

I'm trying a Raspberry Pi for this testing so only have a USB3 interface
available.  Seems to be fast enough but maybe that's why it's giving numbers
that seem odd to you?


> The list of WD drives using SMR as drive-managed is published. See:
> 
> https://blog.westerndigital.com/wd-red-nas-drives/
> 
> and
> 
>
https://blog.westerndigital.com/wp-content/uploads/2020/07/WD_SMR_SKUs_vDS.pdf
> 
> Your drive is not on the list :)


I wasn't sure that the list was reliable when it came to white label drives,
but it's good to have it confirmed.

Many thanks!

Ian
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