My SolusVM graphs have been showing 8Gb Swap usage even though the RAM is never over 50% used. Is it possible that virtual machines going into swap will reduce the IO of the SSD?

  • Your first action should be that you set the swappiness parameter to 0 - i.e. swap only on out-of-memory condition. Furtheron you should avoid swapping to ssd or any other flash device, because wear leveling will reduce the lifetime of your device. – ott-- Sep 8 '13 at 19:29

If you're swapping to the SSD, yes. Swap uses IOs; even SSDs, while not seek limited, still have IO limits. Granted, pageins/pageouts from SSDs are going to be very quick, so unless a VM is thrashing, it's not likely to affect IO that much. A thrashing vm might do more than 1k IOPs. Your SSD is probably rated for >30k IOPs. Then again, your SSD also has a finite write durability, so even under limits, it's not preferable to allow that.

| improve this answer | |
  • Is there any way to prevent/limit IO of OpenVZ virtual machines? I have an IOPriority of 4 set in SolusVM, but I do believe there are certain users completely abusing the IO. – user3180 Sep 8 '13 at 18:24
  • That's a completely different question, but depending on your kernel version, yes. Look into linux cgroups, specifically the blkio controller (linux kernel docs for cgroups blkio). I don't know openvz's particular mechanism for installing cgroup limits, but I know it enables them by default in newer userspaces (/proc/vz/{cgroupstuff}). To check where they are use mount | grep cgroup. You should be able to add a controller to a process in-flight, if needed, assuming it doesn't have that controller from another group. – Andrew Domaszek Sep 8 '13 at 19:02

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.