Set usb flash drive as non rotational drive

Question

I'm trying to optimize the IO schedulers and to use a proper scheduler for rotational and for non rotational drives (different). When I run:

cat /sys/block/sd*/queue/rotational

I get:

1    <-- for sda
1    <-- for sdb

although sdb is the usb flash drive and it shouldn't be rotational.

$ udevadm info -a -n /dev/sda | grep queue
ATTRS{queue_depth}=="31"
ATTRS{queue_ramp_up_period}=="120000"
ATTRS{queue_type}=="simple"

$ udevadm info -a -n /dev/sdb | grep queue
ATTRS{queue_depth}=="1"
ATTRS{queue_type}=="none"

so there is no such attribute as:

ATTR{queue/rotational}=="0" or ...=="1"

Answer 1

Yes it's a wired and confusing issue; here's the corresponding kernel bug 90761 (reported 2015) and a 2019 blog post investigating this. Presumably, it's just a cosmetic issue, as the traditional IO-schedulers have all been superseded by mq-deadline.. However, with considerable head-scratching, I came up with an applicable rule, so I thought I might just as well post it here.

/etc/udev/rules.d/usb-flash-drive-non-rotational.rules:

# Try to catch USB flash drives and set them as non-rotational. Probably no impact whatsoever : /
# c.f. https://mpdesouza.com/blog/kernel-adventures-are-usb-sticks-rotational-devices/

# Device is already marked as non-rotational, skip over it
ATTR{queue/rotational}=="0", GOTO="skip"

# Device has some sort of queue support, likely to be an HDD actually
ATTRS{queue_type}!="none", GOTO="skip"

# Flip the rotational bit on this removable device and give audible signs of having caught a match
ATTR{removable}=="1", SUBSYSTEM=="block", SUBSYSTEMS=="usb", ACTION=="add", ATTR{queue/rotational}="0"
ATTR{removable}=="1", SUBSYSTEM=="block", SUBSYSTEMS=="usb", ACTION=="add", RUN+="/bin/beep -f 70 -r 2"

LABEL="skip"

Answer 2

You can run hdparm -I for each of your disks:

hdparm -I /dev/sda
hdparm -I /dev/sdb

If the output of the hdparm -I line includes a line like:

Nominal Media Rotation Rate: Solid State Device

that would indicate the drive is non-rotational, using information from ATA-style IDENTIFY response.

But apparently there is another way to query this information too, and the kernel seems to prefer it. If you have the sg3_utils package installed, you could use this command to make a query that is identical to what the kernel does (at the time of this writing at least):

sg_inq --vpd --page=0xb1 /dev/sda

If the response includes the line:

Non-rotating medium (e.g. solid state)

...then, and only then will the /sys/block/sd*/queue/rotational attribute be set to 0.

If your USB flash drive is USB2, any scheduler-based optimizations are likely going to be overwhelmed by the USB protocol inefficiency. Only worry about this if you have an actual USB3 SuperSpeed drive.