On Thu, Sep 22, 2022 at 7:11 PM Nick Neumann <nick@xxxxxxxxxxxxxxxx> wrote: > > On Sat, Sep 10, 2022 at 3:28 AM Damien Le Moal > <damien.lemoal@xxxxxxxxxxxxxxxxxx> wrote: > > You can use write-long, to "destroy" sectors: you will get errors when > > attempting to read the affected sectors. But that is a really big hammer. A > > simpler solution is to use dm-flakey to create "soft" IO errors. > > Thank you for mentioning this - I'm not a linux veteran so I did not > know about these tools. > > I tried dm-flakey, but when the device is down, the errors are > returned immediately. I also looked at dm-delay, and that actually > worked pretty well for getting fio to sit and wait on an I/O. > > Unfortunately I have a hard time getting the delay to be "big". The > time it takes to add the delay rule appears to be a linear function of > the amount of delay, with a very big constant factor. A half second > delay takes 11 seconds to add, and a 5 second delay takes 112 seconds: > sudo time dmsetup create test9 --table "0 1024 delay /dev/nullb1 0 500 > /dev/nullb1 0 0" > 0.00user > 0.00system > 0:11.28elapsed > ... > sudo time dmsetup create test10 --table "0 1024 delay /dev/nullb1 0 > 5000 /dev/nullb1 0 0" > 0.00user > 0.00system > 1:52.70elapsed > > And unfortunately something breaks at some point, as my attempt to do > a 70 second delay had not finished after 2 hours. I'm experimenting > right now to try to find a smaller but still big value that is useful > for testing the nvme timeout/retry defaults. I've seen code snippets > online though that set the delay to 100 seconds, so I'm at a loss why > the time to do it is growing so large on my system. > Hi Nick, If you're trying to create an error at an arbitrary location, at an arbitrary time, you might be interested in using the dm-dust target. The documentation in the admin-guide for dm-dust [1] has information on the command interface that the target uses (via the "dmsetup message" command) in order to set up a specific failure scenario for a test device. Thanks, Bryan [1] https://www.kernel.org/doc/html/v5.19/admin-guide/device-mapper/dm-dust.html
