Re: Should nossd mount option be used for an HDD detected as non-rotational?

[Andrei Borzenkov <arvidjaar@gmail.com>]

13.07.2019 12:22, R. Schwartz пишет:
> My HDD (one partition, BTRFS) reports itself as non-rational:
> 
>     $ cat /sys/class/block/sda/queue/rotational
>     0
> 
> According to btrfs(5), by default, BTRFS detects this value and turns on
> SSD optimizations for the HDD. Naturally, I'm puzzled...
> 
> My question is: should I use the nossd mount option for the HDD?
> 
> Following is more details about this HDD.
> 
> It's a recent Western Digital Blue 2TB HDD, model WD20EZAZ. Given its
> cache size is a rather large 256MB, some people say it's likely an SMR
> (shingled magnetic record) HDD.
> 
> Since Host-Managed and Host-Aware SMR HDDs support the `REPORT_ZONES`
> ATA/SCSI command, I ran this test using `sg3_utils`:
> 
>     # sg_rep_zones -R /dev/sda
>     Report zones command not supported
>     sg_rep_zones failed: Illegal request, Invalid opcode
> 
> Therefore, _if_ it's SMR, it must be Drive-Managed SMR.
> 
> So is there a good reason why the HDD reports itself as non-rotational?

kernel sets non-rotational flag according to Medium Rotation Rate field
in Block Device Characteristics VPD page (0xb1). What

sg_vpd -p bdc /dev/xxx

says?

> Does it have to do with SMR?
> 
> Additioanlly, the HDD is connected through a SATA to USB connector. I
> original suspected it was an issue with the connector, but I tested with
> other HDDs with the same connector and they all report as rotational.
>