So far I know that cat /sys/block/<devicename>/queue/rotational will tell me whether my drive is a SSD or HDD. Is there something similar to find out if it uses SMR (Shingled Magnetic Recording)?


The only way to be sure is to benchmark the drive with enough random write access. "drive managed" SMR is supposed to be totally transparent to the host computer and sometimes manufacturers fail to mention SMR. However, the "transparent" is only about logical behavior, not performance (or latency).

I'd suggest following. Run fio as follows (first cd to directory on the disk to test because following will create benchmark test file in the current working directory):

fio --name TEST --eta-newline=5s --filename=fio-tempfile.dat --rw=randwrite --size=500g --io_size=1500g --blocksize=10m --ioengine=libaio --iodepth=1 --direct=1 --numjobs=1 --runtime=3600 --group_reporting

This example will create 500 GB file and select random location within it and write 10 MB of random data. It then repeats the test for up to 1 hour or until 1.5 TB has been written. Watch the ETA lines that look something like this:

Jobs: 1 (f=1): [w(1)] [20.0% done] [0KB/40960KB/0KB /s] [0/4/0 iops] [eta 00m:28s]

The above command will emit a new ETA line every 5 seconds. Look at the speed and IOPS between the slashes (40960KB and 4) above. For SMR drive you should get good values first (100MB+/s and 10+ IOPS) but as the test goes on and the internal cache of SMR drive fills up (usually around 20 GB) the performance will go all over the place. Sometimes it will be near the starting speed, sometimes it will be long periods of time around 0 MB/s and 0-1 IOPS. There should be never errors, though.

Be warned that SMR drives will get slower when used or benchmarked! Some drives support TRIM command and fstrim may help to get the drive speed back to original.

Even without TRIM, a well done "drive managed" SMR will acquire its original speed once left alone powered for long enough. You might need to disable spinning down the disk (power management) if it goes to sleep before the internal cache has been fully flushed to SMR area. For the Seagate SMR drives I've used, full flush of the cache seems to take around half an hour. During this time the drive will sounds like it's writing data even though nothing is written to drive by the computer. Unfortunately, I don't know any way to query the status of flushing from the drive. Either listen to drive sounds or simply wait for long enough.

| improve this answer | |

Modern versions of sg3_utils have a command sg_rep_zones, which will interrogate the drive and ask about its SMR configuration. You may have to build this manually if your distribution doesn't have a recent version.

That can tell you definitively if the drive is SMR.

However, even if the command reports Report zones command not supported, that doesn't tell you for sure that the drive isn't SMR. Some SMR drives use "drive managed" SMR, which means that the drive handles everything magically and you supposedly don't need to worry about it. In this case, it wouldn't necessarily support the report zones command.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.