How to limit CPU usage while tar'ing a large file on a mounted NTFS partition?

Question

I currently tar -cvf a 600gb folder, on the background, without compression.

I noticed that my ubuntu lags so much during this process, that it becomes practically unusable. When I top I see that

60% of my CPU is taken a mount.ntfs command and 15% of my CPU by the tar.

How can I limit the CPU usage of those two to let's say 30% and 10%, so that I can actually use my system at the same time?

You could use `nice` to set process scheduling. See `man nice` for more info. — Panki, Nov 24 '20 at 11:48
`nice` could be useful too, but here it seems you need `ionice` because the perfomance degredation you see is probably more I/O usage related than CPU. Related: https://unix.stackexchange.com/questions/437977/linux-extracting-tar-dramatically-slows-down-server — thanasisp, Nov 24 '20 at 11:56
@thanasisp @panki I am "nicing" the tar command `nice -n 5 tar -cvf backup.tar backup/` , but still mount.ntfs seems to be unaffected. — HelloWorld, Nov 24 '20 at 13:34
try `ionice -c3 -p ` for the pid of your process. It's not the CPU, it's the disk. — thanasisp, Nov 24 '20 at 13:34
`ionice` might not work in this instance since `mount.ntfs-3g` is a userspace process. Might make sense to re-ionice this process instead. — Artem S. Tashkinov, Nov 24 '20 at 13:40
The `tar` process is to be re-ioniced, see also the related post above. — thanasisp, Nov 24 '20 at 13:42
Artem, or you mean that, there could be any implications, over ntfs mount? In general, not for this case only, my simple thought is that if tar requesting is minimized, then this would be enough. — thanasisp, Nov 24 '20 at 14:20

score 2 · Accepted Answer · answered Nov 24 '20 at 14:01

The slowdown is more probably caused by the disk usage rather than CPU usage. tar massively reads and writes for the 600G directory. See also related post.

As the tar process is already running, you have to get its pid, using pidof tar or ps aux | grep tar and renice its I/O priority to class 3.

-c, --class name or number of scheduling class, 0: none, 1: realtime, 2: best-effort, 3: idle

ionice -c3 -p <pid>

This will also make the archiving take longer, as it will use the disk only when it is not being used by other programs.

How to limit CPU usage while tar'ing a large file on a mounted NTFS partition?

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