Can I simulate a slow hard drive?

9,636

Solution 1

Use nbd, the Network Block Device, and then rate limit access to it using say trickle.

sudo apt-get install nbd-client nbd-server trickle

Solution 2

# echo 1 > /proc/sys/vm/drop_caches

That'll slow you down :)

It'll force you to read from disk, instead of taking advantage of the cached page.

If you really wanted to get sophisticated you could do something like fake a read error every nth time using the scsi fault injection framework.

http://scsifaultinjtst.sourceforge.net/

Solution 3

Have a USB 1.1 hub? Or a slow SD card? They'll get you down to under 10mbps.

Solution 4

You can use a Virtual Machine and throttle disk access ... here are some tips about how do it in Virtualbox 5.8. Limiting bandwidth for disk images https://www.virtualbox.org/manual/ch05.html#storage-bandwidth-limit

Solution 5

This is by no means a complete solution, but it may help in conjunction with other measures: There is an I/O scheduler much like a process scheduler, and it can be tweaked.

Most notably, you can actually choose amongst different schedulers:

~# cat /sys/block/sda/queue/scheduler 
noop anticipatory deadline [cfq] 
~# echo "deadline" > /sys/block/sda/queue/scheduler
~# cat /sys/block/sda/queue/scheduler 
noop anticipatory [deadline] cfq 
~#

deadline may help you get more strongly reproducible results.

noop, as its name implies, is insanely dumb, and will enable you to wreck absolute havoc on I/O performance with little effort.

anticipatory and cfq both try to be smart about it, though cfq is generally the smarter of the two. (As I recall, anticipatory is actually the legacy scheduler from right before the kernel started supporting multiple schedulers.)

View more solutions

9,636

RusGraf

My goal here is usually to document.

Updated on September 17, 2022

Comments

RusGraf over 1 year

I have hunch that a certain intermittent bug might only manifest itself when there is a slow disk read rate. Troubleshooting is difficult because I can't reliably reproduce it.

Short of simply gobbling IO with a high priority process, is there any way for me to simulate having a slow hard drive?
- Jeremy over 13 years
  
  I remember seeing a command to tell harddrives to run at certain bus speeds. I'll see if I can dig it out.
- Jeremy over 13 years
  
  man hdparm take a look at the -X option maybe? There are quite a few things in there you could use to slow down your drive, but some of them risk doing nasty things to the data!
- Jeremy over 13 years
  
  Also, try mounting a network share as a folder (google is your friend), maybe even over wifi, if that is plausible.
- poolie over 13 years
  
  This isn't a direct answer, but: if I had an intermittent bug like this, I would probably try running the process under Valgrind (if it was in a compiled language), because that would likely capture IO race conditions.
- poolie over 13 years
  
  Are you talking about a bug in an application, or the kernel, or a device driver? Or you don't know at all? It might help if you explained more.
- RusGraf over 13 years
  
  @poolie It's this problem. It stopped happening on one computer when I installed an SSD.
- poolie over 13 years
  
  OK, I think it is highly likely to be what Jacob said on that bug, that gnome-settings-daemon is crashing, probably related to the timing of different components starting up.
RobotHumans over 13 years

nice...not technical enough for the +1 but nice
poolie over 13 years

I think this answer is seen as unhelpful because the mere fact that the process is doing lots of IO may be already known, or not a problem in itself. The issue is that there is some kind of timing-related bug in the way it handles those IOs.
The Unix Janitor over 13 years

+1 for a pretty cool solution. however, it's not a real test because you not going to the real hard disk device driver, which where the problem may lie.
poolie over 13 years

I didn't think he was talking about a driver bug, but that was just an assumption. Let's see.
papukaija about 13 years

You should explain what that command actually does.
Rich over 8 years

Is it possible to add the actual command to this answer? At the moment you only show how to install the tools required :)
poolie over 8 years

As the question says, "Short of simply gobbling IO"....
poolie over 8 years

As the question says, "Short of simply gobbling IO"....
Androbin over 6 years

Note: This will only drop the caches once. Then it will immediately start caching again. You might wanna wrap that in a loop.
ppetraki over 6 years

@Androbin I like that idea. You could even add a sleep interval to the loop. Thanks!